INVESTIGATIONS OF CRYSTAL GROWTH PROCESSES IN
THE NIKOLAEV INSTITUTE OF INORGANIC CHEMISTRY
F.A. Kuznetsov, Ya.V.Vasiliev, A.A.Pavlyuk, M.L.Kosinova
Institute of Inorganic chemistry, Siberian Branch of Russian
academy of sciences
3 Lavrentiev Pr. 630090, Novosibirsk, Russia
Abstract
In general our crystal growth program includes studies of staring
material preparation, growth procedures and characterization of obtained
materials. Wide variety of materials is considered. In this presentation
we will be limited to oxide crystals applied as luminescence and laser
materials and to processes of formation of nano size crystals.
Mentioned oxide crystals are grown by Low-thermal-gradient
Czochralski technique. First versions of the method were realized in
NIIC back in early 70s. Method is still in process of development. At the
moment most essential characteristics of the method are:
- high precision weight control of crucible (up to 100 kg);
- perfect cylindrical symmetry of temperature field;
- low axial and radial temperature gradients (0.05-1.0 deg/cm);
- ratio of crystal diameter to crucible diameter about 0.8.
Present possibilities of the method can be characterized by
properties of grown crystals. Thus, for BGO:
- boules size: up to 130 mm in diameter and up to 400 mm in
length (~ 50 kg)
- light output non-uniformity: <12% for 25x25x150 mm3
crystals,
- energy resolution at 662 keV: 9.5 % for 2x2 and 10% for
5x5 cylinders,
- unique optical uniformity: attenuation length ~ 10 m (=480nm),
- radiation hardness: ~ 106 Rad.
Recently large crystals of CWO were grown (length up to 200 mm
and weight up to 10 kg). As it is known from literature large crystals of
this material usually are not sufficiently transparent and are have
pronounced non-uniformity. Our crystals do not have these defects.
1
Energy resolution for 137 Cs determined on cylindrical samples of
30x30 size is less then 6.8%.
Micro crystal formed by phases of three component systems Si-CN and B-C-N were observed in thin films obtained in plasma-chemical
process with elementorganic compounds conaining all the deposited
elements. It was shown that by changing conditions (gas mixture
composition and temperature) gradient nano composite films could also
be prepared.
Introduction
One of major objectives of this meeting is to stimulate cooperation
amongst groups and institutions active in different sectors of science and
technology of materials. So, information on programs of these groups is
essential. This communication describes R&D programs of Nikolaev
Institute of Inorganic Chemistry, Siberian Branch Russian Academy of
Sciences (NIIC) devoted to optical materials.
NIIC is one of the biggest Institutes of Russian Academy of
Sciences involved in materials R&D. Optical materials oriented projects
include investigations of crystal structure, phase diagrams, processes of
phase formations, techniques of materials preparations (crystals, films,
multi component structures, glasses.) structural, compositional and
functional characterization, data collection and modeling.
In this presentation we will be limited to oxide crystals applied as
laser and luminescence materials and to processes of formation of nono
size crystals.
1. Low temperature gradient method of crystal growth
Method of crystal growth we use for obtaining optical crystals
described below is a low temperature gradient version of Czochralski
method (LTG Cz technique). It was developed in the NIIC at the end of
the 1970s for growing of mixed oxide crystals with the general formula
M+R3+[Mo(W)O4]2 where M=Li, Na, K, Rb, Cs, Cu, etc. and R=Ln, Sc,
Y, Cr, In, etc. The method originally was developed by A.A. Pavluk and
later significantly improved in collaboration with Ya.V.Vasiliev and
applied for growing of nearly perfect oxide crystals. Essential features of
the LTG Cz technique are illustrated in Fig. 1. A long platinum crucible
is placed into a three-zone resistance heater, having good bottom and top
2
heat insulation. During the entire process the grown crystal stays inside
the crucible.
Fig. 1. Schematic diagram of the apparatus for crystal growth of oxide crystals
in a low thermal gradient.
Axial and radial thermal gradients in the melt are maintained
within the 0.05–1.0 deg/cm. The crucible is covered with a platinum lid
furnished with a pipe socket through which the pull rod with the crystal
holder is introduced into the crystallization space. Not only does the
platinum lid perform the function of a radiation screen, which is
necessary to decrease thermal gradients, but also the pipe socket works
as a diffusion barrier for volatile species and it effectively reduces the
rate of evaporation and decomposition of melt. The effect of such a
device on the mass loss may be almost unnoticeable; however, the
crystal quality essentially improves. The LTG Cz procedure involves the
use of weighing control at all the stages of growth process including
seeding, because the visual control is impossible. The weighing control
also provides process control due to feedback in spite of the decreasing
dynamic stability of crystallization process arising from extremely low
3
thermal gradients. As a result, diameter of the grown crystal is close to
diameter of crucible (Dcrystal.0.8.Dcrucible).
By now LTG Cz technique is successfully applied for growing of
different oxide crystals. In all the cases it was shown that crystals
obtained have higher perfection as compared to crystals grown by other
techniques. Some of oxide crystals have also size not reachable with
other methods. Fig. 2 shows crystal growth division of the Institute.
Fig. 2 Crystal growth shop
At the moment most essential characteristics of the method are:
- High precision weight control of crucible (up to 100 kg)
- Perfect cylindrical symmetry of temperature field,
- Low axial and radial temperature gradients (0.05-1.0 deg/cm)
- Ratio of crystal diameter to crucible diameter about 0.8.
2. BINARY TUNGSTATES AND MOLYBDATES. LASER
CRYSTALS
Binary tungstates and molybdates of different classes were subject
of investigations in IInCh from early 60-s. Research team headed by
P.V.Klevtsov and S.V.Borisov was involved in synthesis and structural
and crystal-chemical studies.
4
Different types of compounds were studied:
- binary molybdates and tungstates with uni- and trivalent cations
(1-3 binary molybdates and tungstates);
- binary molybdates and tungstates with uni- and divalent cations
(1-2 binary molybdates and tungstates);
- binary molybdates and tungstates with two different univalent
cations (1-1 binary molybdates and tungstates).
Most extensively studied is the first type of the compounds (1-3).
About 300 compounds with of general formula M+R3+(EO4)2 were
synthesized. In these compounds M+=Alkali metals ions (Li-Cs), Ag+,
Tl+; R3+= Rare Earth elements (RE elements), Bi, In, Sc, Ga, Al, Fe, Cr
ions; E=Mo or W. The compounds were synthesized mainly by sold
state sintering and deposition form solutions. With application of x-ray
diffraction and thermographic techniques peculiarities of polymorphism
in this class of compounds were revealed. Crystal structures of most of
the synthesized compounds were determined. About 30 different
structural types were identified. Detailed analysis of structures and
character of phase transitions in the system of 1-3 binary molybdates and
tungstates is given in review article [1]. This article contains many
references for original works of the authors and other researchers.
Main conclusions from the analysis:
a) Various different crystal structures of M+R3+(EO4)2 compounds
form a system of related structural modifications. All the identified
structural types can be grouped into five families.
b) Phase transitions are characterized by increasing of symmetry
with temperature.
c) The main factor in structural modification is the size of ions
(rM+ or rR3+).
d) Only in few cases the studied compounds have no
polymorphism. Transitions between the modifications are mostly of
reconstructive types. It means that crystals of low temperature
modifications cannot be grown from melt. In these cases flux or
hydrothermal method of crystal growth was used in our practice.
Results of crystal chemical studies of 1-2 binary molybdates and
tungstates, which are also promising compounds as functional materials,
are described in review article [2].
Synthesis, methods of crystal growth, crystal structure and some
properties of the next group of binary tungstates and molybdates, 1-1
5
compounds with two different univalent cations, are described in a
number of publications (CsLiMoO4 [3] LiNa3(MoO4)2·6H2O [4],
M+Na3(MoO4)2·9H2O (M+=K, Rb) [5], M+NaMoO4·2H2O (M+=Rb, Cs)
[6]).
Crystal chemical analysis of binary molybdates and
tungstates of different classes as well as of some other complex
oxide and fluoride phases, performed by S.V. Borisov and his
colleagues, led them to a conclusion that in structures with heavy
cations classical structure forming rules, such as principle of
close-packed of anions, are not correctly applicable any more.
Main features of the lattices are better described by considering
space distribution of cations. It was shown that in these structures
with heavy cations a super-structural ordering takes place (See for
example papers [7, 8, 9, 10]). A cation’s sublattice is being formed.
Planes of the sublattice include not only the heavy cations, but also
middleweight and even light cations (like Li+). The cation sublattices
that are different in composition and in symmetry show significant
similarity. Thus, for the case of tungstates, molybdates and also for
tantalates and niobates about a half of known crystal structures have a
cation sublattices of F-type (ideally face centered cubic), about a quarter
of the structures have the sublattice of I-type (body centered cubic).
Possible areas of applications of binary molybdates and tungstates
phases may be determined by considering peculiarities of their crystal
structures or performing experimental investigation of physical
properties. In our practice both ways were used [11].
Considered classes of binary compounds (molybdates and
tungstates) may be useful in designing of different types of functional
materials. Of course, knowledge of their physical properties is far from
completed. By now the most developed applications of these materials
are solid-state lasers. In this area our institute cooperated for many years
with Institute of Crystallography RAS (Moscow) and State optical
institute (St.Petersburg). Lately joint program is organized also with
Institute of Laser Physics Siberian Branch RAS (Novosibirsk). Optical
investigations of many 1-3 and 1-2 molybdates and tungstates doped
with mostly RE elements were performed (See for example papers
[12-21]).
6
It was shown that KY(WO4)2 and KGd(WO4)2 are laser matrices
with outstanding properties. For the case of Nd3+ doped single crystals of
these compounds the properties are illustrated by table 1.
Table 1
Laser properties of M+R3+(WO4)2/Nd crystals at 300oK*
Compound,
length and
diameter of
the crystal
KY(WO4)2
(27 and 2.5)
KGd(WO4)
Concentration
of Nd3+, at.%
Orientation
of laser
axis
2.5
 b
Transition
Wave
length,
A
Generation
threshold,
J
F3/24I11/2
F3/24I13/2
4
F3/24I11/2
10672
13510
10706
0.4
0.9
4
4
2
 a
2
(26 and 4)
10688
1
c
(44 and 4)
4
KLu(WO4)2
3
a
F3/24I11/2 10721
6
4
(16 and 3)
F3/24I13/2 13482
 15
* A.A.Kaminski, S.E.Sarkisov, A.A.Pavluk, V.V.Lubchenko Inorganic
Materials, 16,No 4, 720, 1980
These crystals also are efficient nonlinear materials and this fact
was used in construction of multicolor lasers [22, 23].
Very low value of generation threshold in case of Nd-doped KYW
and KGW crystals is not limited to these crystals only. The same is true
for Pr3+-doped KGW crystals for generation due to 1D2>3F4 transition
with wavelength 1.07 µm [24]. Information on laser properties of
different tungstates and molybdates phases is given in Table 2.
Very essential part of tungstates and molybdates program is
material preparation and especially crystal growth. Different methods of
crystal growth are available at the institute: growth from melt, from flux
or from water solutions at moderate temperatures or in hydrothermal
conditions. Selection of the method is determined by nature of possible
phase transitions in the system and character of phase diagrams of
systems used in the technology. In many cases the compound has a
number of polymorphic modifications and the required phase is not a
high temperature one.
7
Table 2
New laser materials
8
Fig.3 KGd(WO4)2/Nd crystals grown by flux LTG
If the transition leading to this phase is of reconstructive type,
crystals of the phase cannot be obtained starting from stoichiomentric
melt. The same is true for the case of incongruently melting phases.
These situations are common for the considered types of the compounds.
In some cases phases of interest have sufficient solubility in water to use
solution technique for crystal growth (an example is 1-1 type of the
compounds). In many cases the method, which gives the best results, is
crystallization from high temperature solutions in molten salts (flux).
Arrangement of the growth process is shown on fig.1. Large and good
quality crystals of many binary tungstates and molybdates were grown
with use of flux crystallization by LTG Cz technique. Crystals grown at
such conditions are as a rule faceted. Fig.3 shows examples of single
crystals obtained by this technique.
3. Scintillation crystals
A number of substances prospective for preparation of scintillation
crystals were considered in our studies. By now the best results are
9
obtained with preparation of single crystals of two types: bismuth
germinate Bi4Ge3O12 (BGO) and cadmium tungstate CdWO4 (CWO).
Both crystals were grown from melt. In conditions of low
temperature gradient growth interface was well faceted. Fig. 4 shows
this phenomenon for BGO crystals. Details on dependence of crystal
morphology on the growth conditions are described in [25, 26].
Fig. 4 Idealized and actual shapes of BGO solid–liquid interface: (a) growth
along [1 0 0]; (b, c) growth along [1 1 1] direction at deferent depths of
polyhedron immersion
With fully faceted stable interface, it is possible to obtain highquality uniform BGO crystals free of inclusions. X-ray topography study
shows that quite large volumes of crystals are free from boundaries and
dislocations. It can be seen in the literature that BGO crystals grown by
traditional Czohralski method frequently contain inclusions and require
after growth heat treatment to restore stoichiomentry. These problems
are due to overheating of the bottom part of the melt. At conditions of
our method described above the problems are avoided.
10
Absence of overheated parts and suppression of evaporation are
also essential for growth of CWO. In this case difficulty are related to
high volatility of cadmium oxide. At the conditions of LTG Cz this
problem significantly reduced and required access of cadmium oxide in
the melt is only of order of 1%. CWO crystals are transparent and
colorless and do not require after treatment. BGO and CWO crystals are
shown on Fig. 5
b)
a)
Fig. 5. Appearance of BGO (a) and
CWO single crystals grown by LTG
Cz.
Main characteristics of the crystals are following. Crystals of
BGO:
- boules size: up to 130 mm in diameter and up to 400 mm in
length (~ 50 kg)
- light output non-uniformity: <1.2% for 25x25x150 mm3 crystals,
- energy resolution at 662 keV: 9.5 % for .2.x2. and 10% for .5.x5.
cylinders,
- unique optical uniformity: attenuation length ~ 10 m (л=480nm),
- Radiation hardness: ~ 106 Rad.
BGO crystals are produced in an appreciable quantity.
11
Recently large crystals of CWO were also grown (length up to 200
mm and weight up to 10 kg). As it is known from literature large crystals
of this material usually are not sufficiently transparent and are have
pronounced non-uniformity. Our crystals do not have these defects.
Energy resolution for 137 Cs determined on cylindrical samples of
30x30 size is less then 6.8%.
Both BGO and CWO are scintillators of high Z and high density
with an appreciable light output. They are used for construction of
compact detectors of high gamma detection efficiency. Such detectors
have different applications. To name just a few application we can
mention:
- astrophysics, planetology (г-ray astronomy, radiometry and
activation analysis of heavenly bodies);
- physics of high energies (low noise detectors, spectrometers);
- medicine (positron emission and x-ray computer tomography);
- geophysics (radiometric mapping, borehole radiometric and
activation analysis);
- industrial defectoscopy;
- highly sensitive dosimetry (nuclear power plants, storage of
nuclear wastes and so on).
Fig. 6-8 show some examples of applications based of crystals
grown in our institute.
4. Films and microcrystals of Si and B carbonitrides
Essential activity of the institute is related to synthesis,
purification and application of volatile metal organic compounds. List of
types of volatile compounds, which are subject of investigations, is
given below.
- silicon organic compounds: oligoorganosiloxanes (linear, cyclic
and 3d types);
- b-diketonates of metals;
- S-containing chellates (dithiocarbomates, xantogenates);
- volatile boron compounds;
- aliphatic and fluorinated metal carboxilates;
- complexes on the base of polifluorinated thiophenoles of pentaflourobenzoic acid;
- heterometallic carbonil clusters;
- Nb cluster thio complexes.
12
a)
c)
b)
Fig. 6 Positron emission tomography: a) –In hospital, b) detector’s arrays ring,
c) detectors, produced by the Institute
Fig. 7. Belle detector in KEK laboratory Tsucuba.
13
Fig. 8. “Integral” mission a) – Space unit, b) part of IBIS spectrometer made in
the institute
Important application of these compounds for material preparation
is Chemical Vapor Deposition (CVD) processing. In this article we will
limit ourselves to CVD preparation of carbonitrides films and structures.
A variety of techniques is used for this purpose. A promising technique
is plasma chemical deposition. The technique of plasma deposition
provides a route to fabricate multi-component thin films in the
amorphous and nanocrystalline state. These types of films, if they exist
as nanocomposites, can possess improved properties of hardness, wear,
and resistance to oxidation and corrosion. Silicon carbide and silicon
nitride are prospective materials for potential high-temperature structural
applications because of their excellent mechanical property. Both are
high-temperature wide band gap semiconductor materials used as
electrical insulators or diffusion barriers in microelectronic device.
Experimental set up used for preparation of Silicon and boron
carbonitrides films is shown on the Fig. 9.
Fig. 9. General view of set up (RPECVD)
14
The silicon carbonitride films were synthesised by Remote Plasma
Enhanced Chemical Vapor Deposition method (RPECVD) at total
pressure of 6.10-2 Torr and at temperatures of 473-1173 K using
hexamethyldisilazane Si2NH(CH3)6 as volatile single-source precursor in
mixture with ammonia or helium. The films of the B-C-N system have
been synthesised using boron- and nitrogen – containing organic
precursor – triethyl(or methyl)amine borane complex N(C2H5)3:BH3
(TEAB) both with and without ammonia in the temperature range of
673-1073 K.
A wide variety of techniques was used to characterize the films.
Results of investigations are described in [27, 28]. Some selected
properties are demonstrated by fig. 10-11.
Fig. 11 High resolution electron microscopy picture of BCN film
showing “onion-like” structure of the material
Fig. 10 High resolution electron microscopy picture of SiCN nano
particles and AFM image showing surface morphology of fil
15
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
18.
19.
References
P.V.Klevtsov, R.F.Klevtsova Journal of Structural Chemistry 18, No
3, 419-439, 1977 (Russ)
S.F.Solodovnikov, R.F.Klevtsova, P.V.Klevtsov Journal of
Structural Chemistry 35, No 6, 146-157, 1994 (Russ)
R.F.Klevtsova, P.V.Klevtsov, K.S.Alexandrov Proc. of USSR
Acad.of Sci. 255, No 6, 1379, 1980
R.F.Klevtsova ,L.A.Glinskaya ,P.V. Klevtsov Crystallography 33,No
3, 636, 1988
R.F.Klevtsova ,L.A.Glinskaya et al Crystallography 35,No 5, 1095,
1990
P.V.Klevtsov, et. al. 12th Europ. crystallogr. meet. Moscow.,
Abstracts V2, P.96, 1989
S.V.Borisov, N.V.Podberezskaya Stable cation carcasses in
structures of fluorides and oxides. Novosibirsk, Nauka, 1984
S.V.Borisov J. Struct. Chem. 27, No 3, 164, 1986
S.V.Borisov, R.F.Klevtsova Crystallography 32, No1, 113, 1987
S.V.Borisov et.al. in book Crystallogrphy and Crystallochemistry P.
158-170, Moscow, Nauka, 1986
A.A.Pavlyuk, L.I.Yudanova, O.G.Potapova, Inorganic Materials,
Vol.33,No 1,1997,pp.64-67.
A.A.Kaminski, A.A.Pavluk, Inorganic Mater. 31, No 11, 1500, 1995
A.A.Kaminski, A.A.Pavluk, P.V.Klevtsov Inorganic Mater. 13, No 3,
582, 1977
A.A.Kaminski, A.A.Pavluk, T.I. Butaeva Inorganic Mater. 15, No 3 ,
541, 1979
A.A.Kaminski, A.A.Pavluk, et al Inorganic Mater.15, No 11, 2092,
1979
A.A.Pavluk, L.I.Koseeva, K.G.Fomin, Inorganic Mater. 19, No 5,
847, 1983
A.A.Kaminski, P.V.Klevtsov, A.A.Pavluk, IEEE J. Quantum
Electron. 8, No 5, 457, 1972
A.A.Kaminski, A.A.Pavluk, T.I. Butaeva Inorganic Mater. 13, No.8,
1541, 1977
A.A.Kaminski, V.A.Fedorov, A.G.Petrosian Inorganic Materials,
15, No 8, 1494, 1979
16
20. B.M.Aupov, V.I.Protasova, A.A.Pavluk, L.Yu. Kharchenko
Inorganic Materials 22, No 7, 1156, 1986
21. A.A.Kaminski, H.R.Verdun, W.Koecher, F.A.Kuznetsov, A.A.Pavluk
Kvantovaya Electronica 19, 941, 1992
22. V.Mochalov, Optic Eng., 36(6),pp.1660-1669,(1997).
23. I.V.Mochalov, Автореферат диссертации д. ф.-м.н., СПетербург, 2001г.
24. A.A.Kaminski, S.N.Bagaev, A.A.Pavluk Phys. Stat. Sol. (a) 151,
K53, 1995
25. Yu.A. Borovlev, N.V. Ivannikova, V.N. Shlegel, Ya.V.Vasiliev,V.A.
Gusev. Progress in growth of large sized BGO crystals by the lowthermal-gradient Czochralski technique. // Journal of Crystal
Growth. 2001, 229, Issue 1-4, p. 305-311
26. V.S. Yuferev, O.N. Budenkova, M.G. Vasiliev, S.A. Rukolaine, V.N.
Shlegel, Ya.V. Vasiliev, A.I. Zhmakin, "Variations of solid-liquid
interface in the BGO low thermal gradients Cz growth for diffuse
and specular crystal side surface" // J. Crystal Growth, 253 (2003)
383-397.
27. M.L. Kosinova, N.I. Fainer, Yu.M. Rumayntsev, E.A. Maximovski,
F.A. Kuznetsov, M. Terauchi, K. Shibata, F. Satoh. Growth of
homogeneous and gradient BCxNy films by
PECVD using
trimethylamino borane complex. Proceed. CVD XVI and
EUROCVD 14 Conf. 2003, v.2, p. 708 - 715
28. N.I. Fainer, Yu.M. Rumayntsev, A.N. Golubenko, M.L. Kosinova,
F.A. Kuznetsov. Synthesis of nanocrystalline silicon carbonitride
films by remote plasma enhanced chemical vapor deposition using
the mixture of hexamethyldisilazane with helium and ammonia.
Journal of Crystal growth. 2003, v. 248, p. 175 – 179
17