STUDIA UNIVERSITATIS BABEŞ-BOLYAI, PHYSICA, SPECIAL ISSUE, 2003
MAGNETIC AND IR SPECTROSCOPIC BEHAVIOUR OF SOME GLASSES
CONTAINING GADOLINIUM AND NEODYMIUM IONS
E.Culea1, I.Bratu2, Lidia Pop1
1
Technical University of Cluj-Napoca, Physics Dept.,
str.C.Daicoviciu, nr.15, 3400 Cluj-Napoca, Romania email: eugen.culea@phys.utcluj.ro
2
National Institute for Research and Development of
Isotopic and Molecular Technologies, str.Donath, nr.65103, 3400 Cluj-Napoca, Romania e-mail:
Glasses of the xR 2 O 3 (1-x)(3Bi2 O 3PbO) vitreous system with R = Gd
and Nd and 0 ≤ x ≤ 0.30 were obtained and studied by IR spectroscopy,
density and magnetic susceptibility measurements. IR and density
measurements show that addition of R ions produces structural changes
and these ions play a network modifier role in the host glass matrix.
Magnetic susceptibility data show that the R3+ magnetic ions are present
as isolated species for low x values and as both isolated and exchange
coupled species for higher x values.
Introduction
Rare-earth elements in glass have been widely studied due to their important
applications for optical telecommunication, laser technology and immobilisation of
radioactive materials [1].
A lot of studies were reported over the past several decades on the spectroscopic
properties of Nd3+ ions incorporated in a large variety of vitreous matrices [1-4].
The important interest concerning these glasses is related to the capacity of the
Nd3+ ions in producing strong infrared fluorescence radiations, which make these
materials possible candidates in high power laser applications.
Glasses containing other rare-earth elements such as gadolinium were studied
especially due to their interesting structural and magnetic properties [5, 6].
On the other hand, glasses based on Bi2O3 heavy metal oxide attracted a great deal
of interest due to their important applications in the field of glass ceramics, layers
for optical and electronic devices, thermal and mechanical sensor, reflecting
windows, etc. [7, 8]. Due to the small field strength of Bi3+ ions, Bi2O3 cannot be
considered as a network former oxide. However, in combination with other oxides
(i.e., B2O3 or PbO), glass formation is possible in a relatively large composition
range [8]. The interest for Bi2O3 as a network forming oxide is increased by the
fact that bismuth ions are known to have more than one stable coordination
generating several structural units.
In this view, we considered the 3Bi2O3.PbO glass matrix to be a very interesting
host for the gadolinium and neodymium ions. In order to obtain information
concerning magnetic and spectroscopic properties of bismuthate glasses containing
gadolinium and neodymium ions we studied the xR2O3(1-x)(3Bi2O3.PbO) glass
EUGEN CULEA, ION BRATU, LIDIA POP
system, where R = Gd and Nd, by means of IR spectroscopy, magnetic
susceptibility and density measurements.
Experimental
Samples of the xR2 O3(1-x)[3Bi 2O3PbO] vitreous system where R =Gd and Nd
and x = 0.02, 0.05, 0.10, 0.15 and 0.20 (in addition, x=0.25 and 0.30, for the R=Nd
samples) were obtained using reagent grade Bi 2O3 , PbO, Gd2O3 and Nd2O3. First,
the base 3Bi 2 O3 PbO glass was prepared by mixing suitable amounts of Bi 2O3 and
PbO and melting the mixture at 1100oC for 15 minutes. The melt was quenched on
a refractory steel block. The obtained base glass was crushed and powdered.
Appropriate amounts of Gd2O3 or Nd2O3 and 3Bi2 O3PbO glass powder were
mixed and milled in an agate ball mill for 30 minutes. Then, the mixtures were
melted at 1100oC for 15 minutes. The glass samples were obtained by pouring the
melts on stainless steel.
X-ray diffraction investigation of the samples did not reveal crystalline phases.
IR spectra were recorded in the 4002000 cm-1 range with an EQUINOX 55
spectrophotometer using the KBr pellet technique.
Magnetic susceptibility measurements were performed on a Faraday type balance
in the 80 to 300 K temperature range.
Density measurements were performed using the picnometric method with water as
the reference immersion liquid.
Results and discussion
Fig.1 shows the infrared absorption spectra recorded for some of the xR 2 O3(1x)[3Bi 2 O3 PbO] glasses with R = Nd.
1.0
7
6
Absorbance units
0.9
0.8
5
0.7
4
3
0.6
2
0.5
1
0.4
0.3
0.2
0.1
0.0
2000
1800
1600
1400
1200
1000
800
600
400
-1
Wavenumber (cm )
Fig. 1 IR absorption spectra of some of the xR 2 O 3 (1-x)[3Bi2O 3 PbO] glasses with R = Nd
(x=0 (1), x-0.05 (2), x=0.10 (3), x=0.15 (4), x=0.20 (5), x=0.25 (6) and x=0.30 (7)).
MAGNETIC AND IR SPECTROSCOPIC BEHAVIOUR OF SOME GLASSES CONTAINING GADOLINIUM
AND NEODYMIUM IONS
A simple inspection of the spectral features of the spectra presented in Fig.1 shows
that they are those characteristic of the base glass matrix, 3Bi2 O3PbO, and no
dramatic changes occur with increasing the Nd2O3 content, x, of the samples.
The same spectral features and weak modifications determined by varying the
rare-earth oxide content were evidentiated for the glasses with R = Gd.
Some of the IR spectral features observed for the xR2 O3 (1-x)[3Bi 2 O3 PbO]
glasses studied by us are associated to the structural units involving the Bi3+ cation.
Thus, several fundamental vibrational bands, such as those at about 460, 600 and
855 cm-1, are assigned to the Bi-O group [9-11].
The absorption band from 855 cm-1 represents the convolution of the absorption
bands reported for different bismuthate glasses at 847 and 860 cm-1, assigned to the
total symmetric stretching vibrations of the [BiO3] and [BiO6] polyhedra,
respectively [9-11]. In bismuthate glasses the [BiO3] polyhedra play the glass
network former unit role while the [BiO6] play the glass network modifier unit role
[10]. Based on the IR spectra obtained for the xR2 O3 (1-x)[3Bi2 O3PbO] glasses,
we assumed that the structure of these glasses is built up of both [BiO3] and [BiO6]
structural units.
The increase of the R2O3 content, x, of the xR2 O3(1-x)[3Bi2 O3PbO] samples
determines the increase of the absorption band at 855 cm-1 and its slow shift to 850
cm-1. This suggests the increase of the amount of [BiO3] structural units with
increasing x and is due to the increase of the number of nonbridging oxygens
provided by the R3+ ions, having as effect the conversion of [BiO6] into [BiO3]
structural units. Thus, the presence of gadolinium or neodymium ions influences
the surrounding of the Bi3+ cations favourizing the formation of [BiO3] units. In
this view we mention two important facts that were previously reported [9]: (i) the
bonding strength of Bi-O is higher in the [BiO3] units than that in the [BiO6] units
and (ii) the degree of the connectivity of the glass network increases with
increasing number of [BiO3] polyhedra.
The IR absorption band from 460 cm-1 is also related to the [BiO6] polyhedra [11].
The increase of the Nd2O3 content of the xR2 O3(1-x)[3Bi 2O3PbO] glasses with
R=Nd determines a slow shift of this band to higher wave numbers, namely to
471cm-1 for x=0.30. This is due to the increase of the degree of distorsion of the
[BiO6] polyhedra with increasing the Nd2O3 content of the samples.
The IR spectra of the xR2 O3 (1-x)[3Bi 2 O3 PbO] glasses contain also some spectral
features that are not related to the structural units involving Bi 3+ cations. Thus, the
absorption band at about 700 cm-1 is due probably to the vibrations of the Nd-O
group (the IR spectra of the crystalline Nd2O3 shows an absorption band at 655 cm1
assigned to the Nd-O vibrations).
The structural changes observed by varying the R2O3 content of xR2 O3(1x)[3Bi 2 O3 PbO] glasses and evidentiated by the IR investigation suggest that the
gadolinium and neodymium ions play a network modifier role in these glasses.
Such a behaviour was previously reported for other rare earth ions glasses, too
[12].
EUGEN CULEA, ION BRATU, LIDIA POP
6
3
Density (g/cm )
Fig.2 shows the variation of density as function of the neodymium ion content of
the xR2O3(1-x)[3Bi 2 O3PbO] glasses. The estimated error for the determined
density values was less than 0.02 g/cm3.
5.8
5.6
5.4
5.2
0
0.05
0.1
0.15
0.2
0.25
x
Fig. 2 Compositional variation of the density for some of the xR 2 O 3(1-x)[3Bi 2O 3PbO]
glasses with R = Nd () and R=Gd (■).
The addition of the heavy rare-earth ions to an inert glass matrix would lead to a
linear increase of the density with respect to x due to the higher number such
accommodated in the host matrix. Fig.2 shows a very non-regular density-rareearth oxide content dependence of the xR2 O3(1-x)[3Bi 2O3PbO] glasses. This
behaviour suggests that a more complicated mechanism, implying also the
structural changes that occur with increasing rare-earth oxide content of the
samples, must be considered to explain the density-composition dependence. Thus,
density data support the assumption based on the IR spectroscopy data that
increasing the rare-earth oxide content of the xR2 O3 (1-x)[3Bi 2 O3 PbO] glasses
produce structural changes in the host glass matrix.
Fig.3 presents the dependence of the reciprocal magnetic susceptibility, –1, as
function of temperature for some of the xR 2 O3(1-x)[3Bi 2O3PbO] glasses with
R=Gd. The data collapse to straight lines indicating a Curie or a Curie-Weiss type
behaviour, described by
-1 = (T-p)/C
(1)
where C is the Curie constant and p is the paramagnetic Curie temperature and T
is the temperature. The same behaviour was find for all the xR2 O3(1x)[3Bi 2 O3 PbO] glasses studied in the present paper.
The magnetic behaviour of the xR2O3(1-x)[3Bi 2 O3PbO] glasses was assumed to
MAGNETIC AND IR SPECTROSCOPIC BEHAVIOUR OF SOME GLASSES CONTAINING GADOLINIUM
AND NEODYMIUM IONS
3+
Inverse magnetic susceptibility
x10 2(mol/emu)
be due to the presence of the R ions. The 3Bi2 O3PbO host glass matrix was
found diamagnetic and the experimental magnetic susceptibility data obtained for
the xR2 O3(1-x)[3Bi 2O3PbO] glasses were corrected taking into account this
diamagnetic contribution.
7
6
5
4
3
2
1
0
0
100
200
300
400
T (K)
Fig. 3 Compositional variation of the density for some of the xR 2 O 3 (1-x)[3Bi 2O 3PbO]
glasses with R = Gd (x=0.02 (), x=0.05 (■), x=0.10 (▲) and x=0.15 (o)).
The compositional dependence of the paramagnetic Curie temperature, p, is given
in Fig.4.
The analysis of magnetic susceptibility data and of the data presented in figure 4
suggests that for the xR2 O3(1-x)[3Bi2 O3PbO] glasses with 0.02x0.05 the
3+
magnetic R ions are isolated and no magnetic order is present. The glasses with
x0.05 show a mictomagnetic type behaviour, where both isolated and exchange
coupled neodymium ions are present in the glass matrix.
The negative and small values of the paramagnetic Curie temperature p (/p/  9
K for the R=Gd samples and /p/  25 for the R=Nd samples) for x0.05 (see
3+
Fig.4) suggest that the exchange interactions between the R ions are weak and
predominantly antiferromagnetic.
The C values were used to calculate the magnetic moment of the R3+ ions present
in the xR2 O3(1-x)[3Bi 2 O3 PbO] glasses, . The obtained  values were very close
to the values corresponding to the free R3+ ions, namely 3.68B for neodymium and
7.9B for gadolinium, where B is the Bohr magneton [13, 14]. This behaviour is in
agreement with the assumption of weak antiferromagnetic interactions between the
R3+ ions.
EUGEN CULEA, ION BRATU, LIDIA POP
30
-Paramagnetic Curie temperature
(K)
25
20
15
10
5
0
0
0.05
0.1
0.15
0.2
0.25
x
Fig.4 Compositional variation of the paramagnetic Curie temperature of xR 2 O 3(1x)[3Bi 2 O3 PbO] glasses with R=Gd ( ○ ) and Nd (  ).
No composition dependence of  was observed for the xR2O3(1-x)[3Bi2 O 3PbO],
in agreement with the data reported for other oxide glasses containing other oxide
glasses containing neodymium and gadolinium ions [15, 16].
Finally, note that the structural modifications produced by increasing the
neodymium and gadolinium ion content of the xR2O3(1-x)[3Bi 2O3 PbO] glasses
seems to exert a neglectible influence on their magnetic behaviour.
Conclusions
IR spectroscopic investigation of xR2 O3(1-x)[3Bi 2 O3 PbO] glasses with R=Gd
and Nd shows that variation of the rare-earth oxide content of the samples, x,
produce some structural changes of the host glass matrix. Density data support this
assumption.
Magnetic susceptibility data show that at low rare-earth oxide content (x0.05)the
xR2O3(1-x)[3Bi2 O3PbO] glasses present a Curie type paramagnetic behaviour,
while for higher x values present a Curie-Weiss type behaviour.
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