RIGA TECHNICAL UNIVERSITY
Faculty of Material Science and Applied Chemistry
Ilze SMELTERE
Doctoral program „ Material Science”
LEAD-FREE FERROELECTRIC
CERAMICS BASED ON ALKALI
NIOBATES
Summary of the Doctoral Thesis
Scientific dissertation advisors:
Dr. habil. phys., Professor
M.KNITE
Dr. habil. phys.
A. STERNBERG
Riga 2013
Smeltere I. Lead-free ferroelectric ceramics based on
alkali niobates. Summary of the doctoral thesis.-R.:
RTU, 2012. - pp. 27
Printed according to the resolution of Institute of
Technical Physics on January 17th, 2013, protocol
No.1
This work has been supported by the European Social Fund within the project
«Support for the implementation of doctoral studies at Riga Technical University»
2
THE DOCTORAL THESIS IS SUBMITED FOR AWARD OF
DOCTORAL DEGREE IN ENGINEERING SCIENCES AT
RIGA TECHNICAL UNIVERSITY
The thesis for doctoral degree in engineering sciences is to be publicly defended on
June 5th 2013, at 1400 at the Riga Technical University, Faculty of Material Science
and Applied Chemistry 14/24, room 272.
OFFICIAL REVIEWERS:
Dr.sc.ing., Dagnija Loca
Riga Technical University, Riga Biomaterial Innovation and Development Center
Dr.sc.ing., Ruta Svinka
Riga Technical University, Institute of Silicate Materials
Dr.phys., Proffesor Juras Banys
Vilnius University, Laboratory of Phase Transitions Dielectric Spectroscopy
CONFIRMATION
I confirm that I have developed the present Doctoral Thesis, which is submitted for
consideration at Riga Technical University for scientific degree of the doctor of
engineering sciences. The Doctoral Thesis has not been submitted at any other
university for the acquisition of a scientific degree.
Ilze Smeltere ...............................................
Date ....................................................
3
ACKNOWLEDGEMENT
I would like to thank my dissertation scientific advisors professor Dr.habil.phys.
Maris Knite and Dr.habil.phys. Andris Sternberg.
I am grateful to my colleagues from Laboratory of synthesis and processing (Institute
of Solid State Physics) Maija Antonova, Anna Kalvane and Maris Livinsh, and of
course all the colleagues from Ferroelectric division. Thanks to colleagues from
Institute of Physics, Pedagogical University Krakow, Poland, and Dr.phys. Barbara
Garbarz-Glos in particular.
I send my deepest love to my parents and brothers family as well as to all of my
friends for the support and believing in me.
I would like to thank European Social Fund projects «Support for the implementation
of doctoral studies at Riga Technical University» as well as “Multidisciplinary
Research in Biomaterials Technology of New Scientist Group” and UNESCO
L`ORÉAL scholarship for women in science for the financial support.
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CONTENT
GENERAL DESCRIPTION ......................................................................................... 6
Introduction................................................................................................................ 6
The challenge of the topic.......................................................................................... 6
Aim of the work ......................................................................................................... 6
Conferences and Publications .................................................................................... 7
CONTENT OF THE DOCTORAL THESIS ................................................................ 8
Overview on the literature............................................................................................. 8
Experimental.................................................................................................................. 9
Results and discussion................................................................................................. 10
KNN ceramics synthesis .......................................................................................... 10
Pure KNN................................................................................................................. 11
(K0.5Na0.5)Nb1-xSbxO3 ............................................................................................... 13
(1-x)(K0.5Na0.5)Nb1-ySbyO3-xBaTiO3 ....................................................................... 17
CONCLUSIONS ......................................................................................................... 21
THESIS........................................................................................................................ 22
References ................................................................................................................... 23
List of publications ...................................................................................................... 24
List of full text scientific papers in conference proceedings ...................................... 25
Patent of Republic of Latvia........................................................................................ 25
List of conferences ...................................................................................................... 25
5
GENERAL DESCRIPTION
Introduction
Ferroelectric ceramics are used in different devices since 1940’s. Hence the market of
ferroelectric ceramics has developed enormously. Ceramics with different
compositions have been produced and modified to adapt the material for a specific
purpose. Lead zirconate titanate PZT having outstanding electromechanical
properties is mentioned for the first time in 1952. Until now materials based on PZT
have dominated the industry of piezoelectric ceramics. However lead is toxic and the
measures for safe utilization need to be taken. Furthermore lead oxide evaporates
easily causing the environmental pollution. European Union directives released in
2004 restrict the use of toxic elements in electric and electronic devices. A lot of
literature sources about lead-free ferroelectric ceramics are available nowadays
however the deeper research is needed in order to substitute lead-based materials.
Lead-free ferroelectric ceramics based on alkali niobates is one of the most promising
material classes. An advantage is higher phase transition temperatures (around
400°C) compared to other lead-free materials with perovskite structure. Potassium
sodium niobate KNN also possess higher piezoelectric properties. The main difficulty
is to obtain fully dense ceramic body; pure densification of KNN sets a limit for the
electrical properties. Therefore there are many studies about possibilities to improve
the densification process. There are several new sintering methods for example spark
plasma sintering or capacitor discharge sintering available but they are much more
expensive than solid state sintering. For industrial production conventional ceramic
technology is more convenient.
The challenge of the topic
Despite the many studies on lead-free ferroelectric ceramics potassium sodium
niobate KNN is still behind the lead-based materials. The main disadvantage is the
pure density compared to lead-based materials. Besides it is difficult to obtain fully
dense ceramic samples via conventional ceramic technology.
Aim of the work
The aim of the doctoral thesis is to produce dense ferroelectric ceramics based on
alkali niobates using conventional ceramic technology.
According to the aim the tasks for the thesis were highlighted:
• to obtain dense ceramics based on alkali niobates whilst guided by the literature
data on producing and modifying ferroelectric ceramics;
• to research the solid state synthesis process;
• to carry out the structure examination;
• to investigate the dielectric, ferroelectric and piezoelectric properties of obtained
materials;
• to analyze and interpret the obtained results.
6
Conferences and Publications
The results of the doctoral thesis have been reported at 24 international and local
scientific conferences, 10 SCI publications and 3 full text scientific papers in
conference proceedings have been published. One patent of Republic of Latvia has
been received.
7
CONTENT OF THE DOCTORAL THESIS
Overview on the literature
Piezoelectric and ferroelectric materials belong to the class of smart materials it
means their properties can be significantly changed by external stimuli [1]. Lead
zirconate titanate PZT and PZT-based ceramics have dominated the market of
ferroelectric materials for the last five decades. However, they contain up to 60 wt%
lead which is toxic and should be replaced wherever it is possible [2]. This is the
reason for present tendency to develop new lead free ferroelectric materials replacing
Pb-based ones [3-5]. Potassium sodium niobate (K0.5Na0.5)NbO3 (KNN) is one of the
most promising candidates with perovskite structure for this aim. KNN exhibits a
morphotropic phase boundary (MPB) at
K/Na 50/50. Compositions close to this
MPB have the best dielectric, ferroelectric
and piezoelectric properties [6]. Potassium
sodium niobate has perovskite structure;
ABO3 unit cell has a monoclinic symmetry
with lattice parameters am=cm>bm, and β>90°
as shown in Fig.1 [7].
Diffusion couple studies confirmed that
+
Na and K+ ions diffuse into Nb2O5 and not
vice versa. XRD analysis of product layers
declared several intermediate compounds
like Na2Nb4O11, K4Nb6O17, K6Nb10.88O30,
K5.75Nb10.85O30. It is found that Na+ ions
diffuse into Nb2O5 more quickly than K+ Fig. 1. Cell structure: a) (K,Na)NbO3 subcell;
b) The projection of the subcell along b axis;
ions which can be explained with c) Four adjacent subcell projections, while omitting Nb and
differences in ionic radii of Na+ and K+, O atoms [7]
respectively 1.39 Å and 1.64 Å [8].
The properties of the final ceramic product could be changed or improved with
the modification of the solid solution. There are several opportunities:
a) the addition of different oxides as sintering aids,
b) by A- or B-site ion substitution with the same valence ions,
c) by A- or B-site ion substitution with different valence ions.
KNN ceramics is a good candidate for substituting lead-based ferroelectric
ceramics in high frequency dielectric devices [9-11]. Solid solutions based on KNN
could also be a potential implant material. Electric charge promotes osteogenesis and
the proliferation of the cells on the material surface what helps in the bone
regeneration process. Tests proved that cytotoxicity of KNN is not considerable, cell
growth on the surface of material is very good [12].
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Experimental
Potassium sodium niobate ceramics (K0.5Na0.5)NbO3 (KNN) were made by
conventional solid-state sintering method from high purity oxides and carbonates.
KNN was modified:
1. Using different oxides (Li2O, ZnO, SnO2, MnO2, V2O5, WO3) of 1 mass %
as sintering aids;
2. By substituting B-site lattice Nb5+ for Sb5+;
3. By making solid solutions from substituted KNN and BaTiO3 (BT).
Technological scheme of lead-free KNN processing is shown below (Fig.2).
Raw materials:
Na2CO3, K2CO3, Nb2O5 ,
Sb2O5, BaCO3, TiO2
Li2O, ZnO, SnO2,
MnO2, V2O5, WO3
Grinding, homogenization
24 h anhydrous ethanol
Synthesis:
850-950°C, 5h
Sintering aids
Grinding, homogenization
24 h anhydrous ethanol
Cold forming
p=100 MPa
Hot pressing
Sintering:
1080-1240°C, 2-5h
2. att. KNN ceramic processing technological scheme
Differential scanning calorimetry (DSC) and thermogravimetry (TG) analysis
were performed in SiC oven within a temperature interval from room temperature to
1200°C with a heating-cooling rate of 20°C/min (NETZSCH STA 449 F3 Jupiter®).
Synthesis kinetic measurements were performed at different temperatures 400°, 450°,
500°, 550°, 600°, 650°C and different holding times 5, 7, 10, 15, 20, 30 min. One
gram of (K0.5Na0.5)NbO3 was used for each experimental series. The outcome of the
solid state synthesis is measured with parameter α, which is the amount of the reacted
material in time. For the evaluating the sintering process high-temperature
microscope HTM analysis was used (EMO-1750-30-K). Densities of the samples
were measured by Archimedes method. The phase structure was investigated with an
9
X-ray diffraction (XRD) analysis (X’Pert Pro MPD, Cu Kα radiation). The
microstructures of ceramics were studied with scanning electron microscope SEM
(Mira/Tescan). Material constants: the Young′s modulus E, the shear modulus G and
the Poisson′s ratio v were measured by an ultrasonic method (UZP-1 INCOVERITAS).
For the dielectric measurements silver or golden electrodes were carried up and
burned at 700°÷750°C. Temperature and frequency dependence of dielectric
permittivity ε and losses tanδ was measured on an impedance analyzer HP4194A
precision LRC meter. P-E hysteresis loops were measured using Sawyer-Tower
circuit. The samples for piezoelectric measurements were poled and piezoelectric
parameters were determined through resonance – anti-resonance technique.
Results and discussion
KNN ceramics synthesis
KNN ceramic samples were prepared by conventional ceramic technology from
powders synthesized via solid state synthesis as showed in equation 1:
½ K2CO3 + ½ Na2CO3 + Nb2O5 → 2(K0. 5Na0.5)NbO3 + CO2↑ (1)
DSC showed the synthesis process of the solid solution. Endothermic reaction at
lower temperatures is associated with absorbed (85°C) and conjugated water (200°C)
evaporation (Fig. 3). Endothermic peaks above 460°C are linked with a beginning of
the solid state reactions when structural changes occur with decomposing of the
carbonates and CO2 evaporation. Synthesis kinetic measurements confirmed these
results. Further follow reactions at ~690° and 745°C, corresponding to niobium oxide
polymorphic transitions and the end of alkali niobate formation.
Fig. 3. DSC and TG analysis for (K0. 5Na0.5)NbO3
10
From thermogravimetry results (TG) it can be seen that starting from 400°C
there is continuous loss of mass associated with CO2 vaporization. Synthesis kinetic
measurements were performed to define more precisely the data from DSC. The
outcome of the solid state synthesis is measured with parameter α, which is the
amount of the reacted material in time. At 400°C α is only a little above 10 %, at
450°C α is about four times higher. At 650°C after holding sample for 30 min amount
of the reacted material is already 100%. Reaction occurs fast in the first few minutes
because the speed depends on reagent concentration. The reaction speed decreases
simultaneously with a decrease in reagent concentration. XRD analysis confirmed the
formation of perovskite phase with a small amount of intermediate compounds only
for samples sintered at 650°C with holding time 30 min.
Pure KNN
Theoretical density of pure KNN is 4.51 g/cm3. Density of air sintered KNN
sample does not exceed 93%. Dielectric permittivity ε of pure KNN reaches the
maximum at temperature 410°C, which is the phase transition temperature from cubic
to tetragonal TC (Curie temperature). One more phase transition from tetragonal to
orthorhombic structure TO-T occurs at 193°C (Fig. 4).
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Dielectric permittivity ε
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Temperature, C
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a)
130 Hz
500 Hz
1 kHz
10 kHz
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800 kHz
1 MHz
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Temperature, C
400
b)
Fig. 4. Temperature and frequency dependence on a) dielectric permittivity ε and
b) dielectric losses tanδ
KNN with oxide dopants
Oxide additives decrease the optimal sintering temperature of KNN ceramics
from 1170°C to 1100 – 1130°C. XRD analysis showed that the addition of sintering
aids did not affect the crystallographic structure of the ceramics significantly. In all
the samples perovskite structure is confirmed, no secondary phase is observed.
The fracture morphology of KNN ceramics containing different kinds of oxide
dopants is demonstrated on Fig. 5. Pure KNN has inhomogeneous structure with
bimodal grain size distribution. It can be seen that all of the doping elements have
different effects on the microstructure of the ceramic samples.
11
a)
b)
c)
d)
Fig. 5. SEM microstructure: a) pure KNN, b) KNN+Li2O; c) KNN+V2O5; d) KNN+MnO2
Cubic or rectangular morphology of the grains with clear grain boundaries can
be seen in ceramics except those, doped with V2O5 and WO3. The addition of V2O5
causes the growth of fine grains with lamellar grain structure. The addition of MnO2
suppresses the grain growth and gives rather homogenous microstructure with grain
sizes of 1-4 µm which can be explained also by lower sintering temperatures.
The temperature dependence of dielectric permittivity ε at 1 kHz frequency is
shown in Fig.6.
Dielectric permittivity ε
8000
pure KNN
SnO2
MnO2
WO3
ZnO
V2O3
6000
4000
2000
0
100
200
300
400
0
Temperature, C
Fig. 6. Temperature dependence on the dielectric permittivity ε for (K0.5Na0.5)NbO3 ceramics with
different sintering aids at 1 kHz
12
The properties of KNN ceramics depend a lot on sintering conditions. We
obtained an interesting result in ferroelectric properties for the ceramics samples
KNN+MnO2 sintered at the same temperature with different holding times (Fig. 7).
The tendency to make antiferroelectric like double hysteresis loop occurs for a
sample with sintering regime 1100°C for 5 h. KNN consists equally from
ferroelectric potassium niobate KNbO3 (KN) and antiferroelectric sodium niobate
NaNbO3 (NN). KN evaporates at lower temperature than NN and it is possible that
after a longer holding time NN dominates in the ceramic composition what causes the
observed effect.
25
20
o
15
1100 C/2h
P, μC/cm
2
10
5
o
1100 C/5h
0
-5
-10
-15
-20
-25
-40
-20
0
20
40
E, kV/cm
Fig. 7. P-E hysteresis loops for KNN+MnO2 samples depending on sintering time
Pure KNN has modest piezoelectric properties. A small amount (0.5 wt%) of
MnO2 improves the properties considerably, increasing d33 from 80 pC/N to 110
pC/N, kp from 0.3 to 0.38, Qm from 60 to 190. The reason for this first of all is that in
the presence of MnO2 the microstructure becomes more homogeneous. Introducing
manganese dioxide in the KNN composition it changes to Mn3O4 while sintering at
high temperature. Mn3O4 is a compound of MnO·Mn2O3, and has two values Mn2+
and Mn3+ with different ionic radii 0.67 Å, and 0.58 Å, respectively. Mn ions enter
into the B-site lattice causing distortion of crystal lattice and oxygen vacancies what
restricts the domain wall motion. We assume that Mn ions and oxygen vacancies
form the defect dipoles. These dipoles align to the polarization direction forming the
local fields.
(K0.5Na0.5)Nb1-xSbxO3
B-site ion Nb5+ partial substitution for Sb5+ and addition of MnO2 as a sintering
aid leads to obtaining of high density ceramic samples.
The chemical composition affects the microstructure of ceramic sample as well
as the sintering conditions. The influence of antimony Sb5+ substitution level on the
microstructure of the samples sintered at the same temperature is shown in Fig. 8.
13
With increasing Sb5+ content ceramics get more dense and with more homogeneous
microstructure.
b
a
c
Fig. 8. The effect of Sb5+ on microstructure of ceramics sintered at 1130°C for x=0.04 (a),
x=0.05 (b) and x=0.06 (c)
For undoped KNN ceramic two sharp phase transitions are observed at 190o and
about 410oC, corresponding to the phase transitions from orthorhombic to tetragonal
(TO-T) and from ferroelectric tetragonal to paraelectric cubic (Tc), respectively. After
the partial substitution of Sb+5 for Nb+5 both of these phase transitions are shifted to
lower temperatures (Fig. 9).
4
16000
(K0.5Na0.5)(Nb1-xSbx)O3 + 0.5mol%MnO2
x=0.05
Dielectric losses tanδ
Dielectric permittivity ε
(K0.5Na0.5)(Nb1-xSbx)O3 + 0.5wt%MnO2
x=0.04
12000
x=0.07
x=0.02
8000
x=0
x=0.10
KNN
4000
0
100
200
300
400
500
a)
0
Temperature, C
x=0.04
x=0.10
2
x=0.05
x=0.07
1
0
0
x=0.02
3
KNN
x=0.00
0
100
200
300
0
Temperature, C
400
500
b)
Fig. 9. Temperature dependence on dielectric permittivity ε (a) and dielectric loss tanδ (b) at 1 kHz
Fig. 10 demonstrates the changes of both phase transitions with increasing Sb5+
level more clearly.
14
450
(K0.5Na0.5)(Nb1-xSbx)O3 + 0.5wt%MnO2
o
Temperature, C
400
350
Cubic
300
250
Tetragonal
200
150
Orthorhombic
100
0,00
0,02
0,04
0,06
x, mole parts
0,08
0,10
Fig. 10. Phase transition temperatures depending on Sb5+ substitution level
Ceramics with small amount of Sb5+ retain the classic ferroelectric characteristics,
and undergo sharp ferroelectric tetragonal to paraelectric cubic Tc phase transition.
The phase transition peak at Tc becomes broadened gradually with increasing x
indicating the appearance of a diffuse phase transition.
Shoulders emerging on the ε(T) curves at lower frequencies may be an evidence
of a structural transition between the orthorhombic phases or a rotational phase
transition related to turning of oxygen octahedrons [a-b+a-].
The obtained results are characteristic for that observed in complex compounds
or solid solutions, in which foreign ions occupy crystallographically equivalent lattice
sites. The break of translational invariance caused by foreign ions/lattice
imperfections leads to extreme broadening of the transition anomalies in these
materials. The phase transition occurs in the temperature range rather than one
specific temperature value and therefore is called diffused phase transition. The
substitution of B-site ions Nb5+ by Sb5+ introduces additional disorder in this site. As
this substitution is isovalent, it does not affect drastically the charge state of the
material. However, the Sb5+ ion size is smaller than Nb5+ ions, it may cause internal
compressive stress and the random elastic fields are expected from this substitution.
These elastic fields, which promote formation of polar regions, are very likely to be
responsible for improvement of dielectric as well as ferroelectric properties of
investigated ceramics. These results are characteristic for complex solid solutions in
which the substitution is performed with the ions of the same value. Those foreign
ions have different radii and atomic mass such deforming the crystal lattice despite
the same value.
The temperature dependence of the remnant polarization Pr obtained from
pyroelectric measurements is shown in Fig. 11. Both Sb or Sb and MnO2 doping
causes a significant increase of Pr. It should be noted that the remnant polarization
remains nonzero up to temperature higher the structural phase transition temperature
15
for KNNS6 and KNNS6+0.5%MnO2, indicating an possible existence of polar
regions above the structural phase transition.
3
-6
5,0x10
-6
4,0x10
Pr, mC/cm
2
2
-6
3,0x10
-6
2,0x10
o
T( C)
1
-6
1,0x10
1- NKN
2- NKNS6
3- NKNS6 +0.5% MnO2
0,0
0
100
200
300
o
400
Temperature, C
Fig. 11. Pr dependence on temperature
P-E hysteresis loops of all Sb5+ substituted (K0.5Na0.5)(Nb1-xSbx)O3 + 0.5 wt%
MnO2 ceramics are well saturated (Fig. 12). Coercitive field EC did not exceed 10
kV/cm, meaning this kind of material is easy to polarize. The highest Pr values have
compositions which showed the best dielectric properties. Different compositions
have different remnant polarization Pr and the highest Pr values reached the same
compositions with the highest εmax.
20
15
P, μc/cm
2
10
5
0
x=2
x=4
x=6
x=7
x=10
-5
-10
-15
-20
-40
-20
0
20
E, kV/cm
Fig. 12. P-E hysteresis loops
16
40
The samples in composition range from x = 0.02 to 0.07 exhibited excellent
piezoelectric properties: piezoelectric coefficient of d33 = 92 ÷ 192pC/N,
electromechanical planar and thickness coupling coefficients of kp = 0.32 ÷ 0.46 and
kt = 0.34 ÷ 0.48, respectively (Fig. 13).
d33, pC/N
200
150
100
50
kt, kp
0
0,5
0,4
0,3
0,00
0,02
0,04
0,06
0,08
0,10
x, mole parts
Fig. 13. Piezoelectric properties depending on Sb5+ substitution level
(1-x)(K0.5Na0.5)Nb1-ySbyO3-xBaTiO3
New solid solutions with chemical formula (1-x)(K0.5Na0.5)Nb1-ySbyO3-xBaTiO3
(x=0.01; 0.015; 0.02; 0.04; y=0.04; 0.07) (KNNSy%-xBT) were made by
conventional solid state sintering. Phase structure changes from monoclinic to
tetragonal with increasing x in NS4. Lattice parameters changes could be related with
smaller cations entering crystal lattice: K+ - 1.64 Å, Na+ - 1.39 Å, Ba2+ - 1.61 Å for Asite, Nb5+ - 0.64 Å, Sb5+ - 0.60 Å, Ti4+ - 0.605 Å for B-site.
Solid solutions with BaTiO3 addition have smaller average grain sizes; the shape
of grains is a little rounded. MnO2 addition suppresses the grain growth even more
and the microstructure is more homogenous which could be the result of lower
sintering temperatures. A little amount of liquid phase is also detected (Fig. 14).
a) 0.99(K0.5Na0.5)Nb0.96Sb0.04O3 – 0.01BT
b) 0.99(K0.5Na0.5)Nb0.93Sb0.07O3 - 0.01BT
17
0.985(K0.5Na0.5)Nb0.96Sb0.04O3 – 0.015BT
0.985(K0.5Na0.5)Nb0.93Sb0.07O3 – 0.015BT
c) 0.98(K0.5Na0.5)Nb0.96Sb0.04O3-0.02BaTiO3
d) 0.98(K0.5Na0.5)Nb0.93Sb0.07O3-0.02BaTiO3
e) 0.96(K0.5Na0.5)Nb0.96Sb0.04O3-0.04BaTiO3
f) 0.96(K0.5Na0.5)Nb0.93Sb0.07O3-0.04BaTiO3
Fig. 14. SEM microstructure for (1-y)(K0.5Na0.5)Nb1-xSbxO3-yBaTiO3+ 0.5wt%MnO2
The EDS and EPMA (Electron probe micro-analyzer) made in the chosen
microregions of the sample surface analysis confirmed the purity and experimentally
assumed qualitative and quantitative composition.
From the high temperature microscope (HTM) measurements it can be seen
what influence has BaTiO3 on the sintering of the ceramic sample (Fig. 15). BaTiO3
has much higher sintering temperatures than Sb-substituted KNN without BT. We
assume that BT engages the sintering process later which is the reason of developing
18
of the shoulder. It also makes broader the ceramics sintering interval which is
significant for KNN-based materials.
Fig. 15. HTM analysis
Material constants: the Young′s modulus E, the shear modulus G and the
Poisson′s ratio v were measured by an ultrasonic method. The highest velocity of the
longitudinal waves was observed for sample KNNS4-1.5BT (VL = 4720.5 m/s). The
transverse wave velocity for this sample is higher then for other samples (VT = 2699.6
m/s). The values of both Young′s modulus E and the shear modulus G are relatively
high taking into account modest densities of the samples (E = 64.96 GPa, G = 25.86
GPa).
The addition of 1 mol% of BT increases the value of dielectric permittivity ε and
decreases TC. In the same time BT decreases dielectric losses. Phase transition
becomes more diffuse while increasing x. Table 1 summarizes the results of dielectric
properties.
19
Table 1
Density and dielectric properties for different compositions
Composition Density
g/cm3
Dielectric
Dielectric
permittivity loss tanδ
ε (room T) (room T)
Tmax
(C°)
γ
S4-1BT
4.51
1400
0.043
305
1.34
S4-2BT
4.44
1240
0.652
270
1.45
S4-4BT
4.34
1380
0.727
178
1.73
S7-1BT
4.31
1800
0.100
245
1.39
S7-2BT
4.34
940
0.490
211
1.57
S7-4BT
4.43
1400
0.549
129
1.76
20
CONCLUSIONS
1. KNN based ceramic powders were obtained by solid state synthesis from
oxides and carbonates.
2. Synthesis kinetic analysis has been performed. Reactions start at 400°C
when the carbonates start to decompose, however, perovskite phase was
obtained at 650°C with the holding time of 30 min.
3. KNN ceramic samples were produced and modified a) using different oxides
as sintering aids; b) substituting B-site cation Nb5+ for Sb5+ ; c) making solid
solutions from substituted KNN with barium titanate BT.
4. The addition of 1 wt% of different oxides (Li2O, ZnO, MnO2, V2O5) reduces
sintering temperature of KNN (from 1170°C to ~1100°-1120°C ). Dense
ceramic samples were obtained resulting into the growth of dielectric
permittivity at the same time phase transition temperature remained the same
(TC=410°C).
5. After the partial B-site Nb5+ substitution for Sb5+ dielectric permittivity
values increased while phase transitions temperature TC is shifted to lower
temperatures with increasing antimony content.
6. The ferroelectric properties of KNN based ceramics are stable in the wide
temperature range. The remnant polarization Pr remains constant up to
temperature of ~300°C then rapidly drops to zero.
7. The samples in composition range from x = 0.02 to 0.07 exhibited excellent
piezoelectric properties: piezoelectric coefficient of d33 = 92 ÷ 192pC/N,
electromechanical planar and thickness coupling coefficients of kp = 0.32 ÷
0.46 and kt = 0.34 ÷ 0.48, respectively.
8. Solid solutions with BT have high dielectric permittivity ε at room
temperature reaching 1240 ÷1800.
21
THESIS
1. Manganese can change the value in the KNN composition while sintering at
high temperature. The defects and oxygen vacancies appearing are pinning
domain walls testified by triple increase in mechanical quality factor Qm.
Manganese ions and oxygen vacancies create defect dipoles along the
polarization axes amplifying the appearance of the local fields. This results into
increase of dielectric, ferroelectric and piezoelectric properties.
2. Because of higher Pauling electronegativity Sb5+ ion forms a stronger covalent
bond with oxygen anion than Nb5+. By substituting Nb5+ for Sb5+ in
(K0.5Na0.5)NbO3 and optimizing the technological parameters dense ceramic
samples are obtained with higher dielectric permittivity εmax, Pr and
piezoelectric coefficient d33 values than found in literature.
3. New solid solutions with chemical formula (1-x)(K0.5Na0.5)Nb1-ySbyO3xBaTiO3 (x=0.01; 0.015; 0.02; 0.04; y=0.04; 0.07) were made by conventional
solid state sintering. Dense ceramic samples were obtained with high dielectric
permittivity ε at room temperature. Presented with a patent.
22
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List of publications
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диэлектрические свойства твердых растворов модифицированного ниобата
натрия и калия// Физика твердого тела – 2012. – Tом 54(5), 934–936.
2. Sitko D., Garbarz-Glos B., Smiga W., Smeltere I., Kalvane A., Bormanis K.
Characterization of Dielectric Anomaly in Solid Solution Based on BaTiO3//
Ferroelectrics – 2011. – Vol. 424., 1–6.
3. Suchanicz J., Smeltere I., Finder A., Konieczny K., Garbarz-Glos B.,
Bujakiewicz-Koronska R., Łatas M., Antonova M., Sternberg A., Sokolowski
M. Dielectric and Ferroelectric Properties of Lead-Free NKN and NKN-Based
Ceramics// Ferroelectrics – 2011. – Vol. 424(1), 53–58.
4. Smeltere I., Antonova M., Livinsh M., Garbarz-Glos B., Zauls V. Synthesis and
characterization of lead-free (1-x)(K0.5Na0.5)Nb1-ySbyO3-xBaTiO3// Integrated
Ferroelectrics – 2011. – Vol. 123(1), 96–101.
5. Suchanicz J., Finder A., Smeltere I., Konieczny K., Jankowska-Sumara I.,
Garbarz-Glos B., Sokolowski M., Bujakiewicz-Korońska R., Pytel K., Antonova
M., Sternberg A.. Dielectric properties of Na0.5K0.5(Nb1-xSbx)O3+0.5MnO2
ceramics (x=0.04, 0.05 and 0.06)// Integrated Ferroelectrics – 2011. – Vol.
123(1), 102–107.
6. Smeltere I., Bormanis K., Sopit A.V., Burkhanov A.I.. Dielectric response in
(K0.5Na0.5) (Nb1-xSbx)O3+0.5 mol%MnO2 ceramics to weak sinusoidal fields of
low and infra-low frequencies// Integrated Ferroelectrics – 2011. – Vol. 123(1),
108–112.
7. Smeltere I., Antonova M., Kalvane A., Grigs O., Livinsh M. The effect of
dopants on sintering and microstructure of lead-free KNN ceramics// Materials
Science (Medžiagotyra) – 2011. – Vol. 17(1), 62–64.
8. Smeltere I., Dambekalne M., Livinsh M., Dunce M., Mishnov A., Zauls V.
Sintering of lead-free (K0.5Na0.5)NbO3 based solid solution// Integrated
Ferroelectrics – 2009. – Vol. 108., 46–56.
9. Dambekalne M., Antonova M., Livinsh M., Kalvane A., Mishnov A., Smeltere
I., Krutohvostov R., Bormanis K., Sternberg A. Synthesis and characterization
of Sb-substituted (K0.5Na0.5)NbO3 piezoelectric ceramics// Integrated
Ferroelectrics – 2008. – Vol. 102., 52–61.
10. Smeltere I., Dambekalne M., Livinsh M., Dunce M., Mishnov A. Influence of
monoxides addition on sintering of sodium-potassium niobates solid solution//
Integrated Ferroelectrics – 2008. – Vol. 102., 69–76.
24
List of full text scientific papers in conference proceedings
1. Smeltere I., Kalvane A., Livinsh M., Antonova M. Processing and properties of
lead-free KNN-based ceramics// ФТТ-2011, Актуальные проблемы физики
твердого тела. Сборник докладов международной конференции, Минск –
2011. – 192–194.
2. Smeltere I., Livinsh M., Antonova M., Kalvane A., Garbarz-Glos B. Dielectric
properties of modified lead-free ceramics based on alkaline niobates// ФТТ-2011,
Актуальные проблемы физики твердого тела. Сборник докладов
международной конференции, Минск – 2011. – 304–306.
3. Smeltere I., Dambekalne M., Antonova M., Livinsh M., Kalvane A., Dunce M.,
Sternberg A.. Synthesis and characterization of substituted (K0.5Na0.5)NbO3 leadfree ceramics// ФТТ-2009, Актуальные проблемы физики твердого тела.
Сборник докладов международной конференции, Минск – 2009. – 272–274..
Patent of Republic of Latvia
Smeltere I., Antonova M., Kalvane A., Livinsh M. Lead-free ferroelectric ceramics
based on potassium sodium niobate and fabrication of the same// 20.07.2012. Pat.,
Nr. 14533.
List of conferences
1.
2.
I.Smeltere, M.Antonova, A.Kalvane, M.Livinsh, M.Dunce, B.Garbarz-Glos,
A.Sternberg. The effect of BaTiO3 on the microstructure and dielectric properties
of Sb-substituted KNN. ISAF-ECAPD-PFM 2012, 9.07-13.07.2012, Averio,
Portugal.
Ilze Smeltere, Maija Antonova, Maris Livinsh, Anna Kalvane, Barbara GarbarzGlos. The effect of BaTiO3 on dielectric and ferroelectric properties of lead-free
ceramics based on KNN. FM&NT 2012, Riga, Latvia.
3.
Ilze Smeltere, Anna Kalvane, Maris Livinsh, Maija Antonova. Processing and
properties of lead-free KNN-based ceramics. SSP-2011 Actual problems of
Solid State Physics, October 17 – 22, 2011, Minsk, Belarus.
4.
Ilze Smeltere, Anna Kalvane, Maija Antonova, Maris Livinsh. Microstructure
and electrical properties of Ta-substituted KNN lead-free ceramics. European
Meeting on Ferroelectricity EMF, June 25 – July 2, 2011, Bordeaux, France.
5.
Ilze Smeltere, Maija Antonova, Marija Dunce, Maris Livinsh, Barbara GarbarzGlos, Vismants Zauls. Electrical and mechanical properties of KNN based leadfree ceramics 19.06. – 24.06.2011. ECERs, Stockholm, Sweden.
25
6.
J.Suchanicz, I.Smeltere, A.Finder, K.Konieczny, B.Garbarz-Glos, M.Antonova,
A. Sternberg. Dielectric and ferroelectric properties of lead-free NKN and NKNbased ceramics. FMNT 2011, April 5 – 8, 2011, Riga, Latvia.
7.
Ilze Smeltere, Maija Antonova, Maris Livinsh, Barbara Garbarz-Glos. Influence
of BaTiO3 on synthesis and structure of lead-free ceramics based on KNN.
FMNT 2011, April 5 – 8, 2011, Riga, Latvia.
8.
Ilze Smeltere, Maija Antonova, Marija Dunce, Maris Livinsh, Barbara GarbarzGlos, Vismants Zauls. Synthesis and properties of (1-x)(K0.5Na0.5)Nb1-ySbyO3xBaTiO3 lead-free solid solutions. Piezo 2011 Electroceramics for End users VI,
February 28 – March 2, 2011, Sestriere, Italy.
9.
Ilze Smeltere, Maija Antonova, Anna Kalvane, Oskars Grigs, Maris Livinsh.
The effect of dopants on sintering and microstructure of lead-free KNN. The
12th International Conference “Advanced Materials and Technologies” and
Summer School “European Doctorate in Physics and Chemistry of Advanced
Materials”, August 27 – 31, 2010, Palanga, Lithuania.
10. I.Smeltere, A.Kalvane, M.Antonova, M.Livinsh, B.Garbarz-Glos, V.Zauls.
Effect of tantalum content on synthesis of lead-free piezoelectric KNN ceramics.
LUP I Lithuanian-Ukrainian-Polish Meeting on Ferroelectrics Physics,
September 13 – 16, 2010, Vilnius, Lithuania.
11. I.Smeltere, M.Antonova, M.Dunce, M.Livinsh, V.Zauls. Effect of MnO2 and
WO3 addition on sintering and properties of lead-free KNN ceramics.
Electroceramics XII. June 12 – 17, 2010, Trondheim, Norway.
12. Ilze Smeltere, Maija Antonova, Maris Livinsh, Barbara Garbarz-Glos, Vismants
Zauls. Synthesis and characterization of lead-free (1-x)(K0.5Na0.5)Nb1-ySbyO3xBaTiO3 FMNT 2010, March 16 – 19, 2010, Riga, Latvia.
13. Ilze Smeltere, Maija Antonova, Anna Kalvāne, Māris Līviņš, Vismants Zauls.
Modificēta KNN cietā šķīduma sintēze un dielektriskās īpašības. LU CFI 26.
Zinātniskā konference, 2010. gada 17. – 19. februāris, Rīga, Latvija.
14. I.Smeltere, M.Dambekalne, M.Antonova, M.Livinsh, A.Kalvane, M.Dunce,
A.Sternberg. Synthesis and characterization of substituted (K0.5Na0.5)NbO3 leadfree ceramics. IV International Scientific Conference Topical Issues of Soild
State Physics. October 20 – 23, 2009, Minsk, Belarus.
15. I.Smeltere, M.Antonova, A.Kalvane, M.Livins, M.Dunce, V.Zauls. The effect of
Sb and Ta substitution on the properties of lead-free KNN ceramics. RTU 50.
starptautiskā zinātniskā konference, 2009. gada 16. oktobris, Rīga, Latvija.
16. Ilze Smeltere, Maruta
Zauls. Influence of
(K0.5Na0.5)NbO3 solid
"Advanced Materials
Lithuania.
Dambekalne, Maris Livinsh, Marija Dunce, Vismants
oxide doping on the sintering and properties of
solution. 11th International Conference – School
and Technologies, August 27 – 31, 2009, Palanga,
26
17. Dambekalne M., Antonova M., Livins M., Kalvane A., Smeltere I., Mishnov A.,
Krutohvostov R., and Bormanis K. Production and dielectric properties of
modified potassium-sodium niobate solid solutions. ECERS 2009, June 21 – 25,
2009, Krakow, Poland.
18. Ilze Smeltere, Maruta Dambekalne, Maris Livinsh, Marija Dunce, Anatoly
Mishnov, Vismants Zauls. Sintering of lead-free (K0.5Na0.5)NbO3 based solid
solution. FM&NT 2009, March 31 – April 3, 2009, Riga, Latvia.
19. I.Smeltere, M.Dambekalne, M.Antonova, M.Livinsh, A.Kalvane, V.Zauls.
Processing and properties of doped (K0.5Na0.5)NbO3 ceramics. Piezo 2009,
March 1 – 4, 2009, Zakopane Poland.
20. I.Smeltere, M.Dambekalne, M.Livinsh, M.Dunce. Influenece of different oxide
addition on synthesis and properties of KNN piezoelectric ceramics. RTU 49.
starptautiskā zinātniskā konference, 2008. gada 13. – 15. oktobris, Rīga, Latvija.
21. Ilze Smeltere, Maruta Dambekalne, Maris Livinsh, Anatoly Mishnov.
(K0.5Na0.5)NbO3 piezoelectric ceramics doped with sintering aids of different
oxides. Electroceramics XI, September 1 – 4, 2008, Manchester, United
Kingdom.
22. Ilze Smeltere, Maruta Dambekalne, Maris Livinsh, Anatoly Mishnov.
(K0.5Na0.5)NbO3 piezoelectric ceramics doped with sintering aids of different
oxides. MIND Multifunctional & integrated piezoelectric devices. MIND
Internal seminar on „Functional characterization of piezoelectric materials. June
19 – 20, 2008, Ljubljana, Slovenia.
23. Ilze Smeltere, Maruta Dambekalne, Maris Livinsh, Marija Dunce, Anatoly
Mishnov. (K0.5Na0.5)NbO3 piezoelectric ceramics doped with sintering aids of
different oxides. FM&NT, April 1 – 4, 2008, Riga, Latvia.
24. M.Dambekalne,
I.Smeltere,
M.Līviņš,
A.Mišņovs.
(K0.5Na0.5)NbO3
pjezokeramikas īpašību uzlabošana ar dažādu oksīdu piedevām. LU CFI 30 gadu
jubilejai par godu veltīta konference, 2008. gada 20. – 22. februāris, Rīga,
Latvija.
27