On solubility of europium monoxide in melts of (NaBr + NaI) system at T = 973 K

J. Chem. Thermodynamics 91 (2015) 136–140

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On solubility of europium monoxide in melts of (NaBr + NaI) system at T = 973 K V.L. Cherginets ⇑, T.P. Rebrova, Yu.N. Datsko, A.L. Rebrov Institute for Scintillation Materials, National Academy of Sciences of Ukraine, Lenin Avenue, 60, Kharkov 61001, Ukraine

a r t i c l e

i n f o

Article history: Received 10 April 2015 Received in revised form 28 July 2015 Accepted 2 August 2015 Available online 5 August 2015 Keywords: Melts Sodium bromide Sodium iodide Europium oxide Potentiometry Solubility

a b s t r a c t Equilibria of EuO dissolution and dissociation in molten (NaBr + NaI) mixtures of 0.77:0.23 and 0.31:0.69 compositions at T = 973 K were studied by potentiometric titration method using Pt(O2)|ZrO2(Y2O3) indicator electrode. The solubility product indices of EuO are (7.81 ± 0.08) and (8.43 ± 0.16) in the melts of 0.77:0.23 and 0.31:0.69 compositions. The corresponding dissociation constant indices are (4.96 ± 0.04) and (5.54 ± 0.06), respectively (all the parameters are in molality). Non-dissociated EuO is the prevailing form in all the saturated solutions of europium monoxide. The decrease of the iodide ion concentration in the melts results in strengthening of EuO dissociation that is explained by introduction of harder Pearson’s base (Br
) in sodium iodide melt. In its turn this increases the fixation degree of Eu2+ in mixed halide complexes. The total solubility of EuO decreases going from NaI melt to the (bromide + iodide) mixtures that is caused by the decrease of ‘physical’ solubility of non-dissociated oxide which occupies hollow spaces of enough large size in the ionic solvents. The quantity of these hollow spaces diminishes at the sequential Br
? I
substitution. Ó 2015 Elsevier Ltd. All rights reserved.

1. Introduction The development of modern materials science necessitates intense searching for new promising materials possessing enhanced functional characteristics. This also concerns optical halide single crystals widely used for different scientific and practical purposes. One of the most popular modern trends in materials science of scintillators consists in the change-over from Eu2+doped single crystals of single ionic halides, e.g., BaI2:Eu2+ [1], CaBr2:Eu2+ [2] to more complex materials: both mixed compounds (CsBa2I5:Eu2+ [3], CsSrCl3:Eu2+ [4]) and solid solutions ({BaBr2 + BaI2}:Eu2+ [5], (CaBr2 + CaI2):Eu2+ [6] etc.). In this relation the solid solutions of (NaBr + NaI) system are attractive as potential substitute of NaI matrix in Tl+- and Eu2+-doped [7] scintillators. As concerns Eu2+ ion, it should be noted that in ionic melts it reveals appreciable affinity to oxide ions [8] that may result in precipitation of EuO form the doped melt and loss of the dopant. Therefore, for prediction of behavior of Eu2+ (EuI2) dopant in melts of (NaBr + NaI) system the information about thermodynamic parameters of the formation of europium (II) oxide is necessary. The determination of the said

⇑ Corresponding author. Tel.: +380 63 7119592; fax: +380 57 3404474. E-mail address: [email protected] (V.L. Cherginets). http://dx.doi.org/10.1016/j.jct.2015.08.001 0021-9614/Ó 2015 Elsevier Ltd. All rights reserved.

parameters by the potentiometric titration of Eu2+ cations with O2
is the purpose of this work. As to the choice of the melt compositions, the following considerations should be mentioned. Since all the earlier studies of Eu2+ acidity in NaI melt have been performed at T = 973 K it seems reasonable to perform the present study just at this temperature. However, considering the phase diagram of (NaBr + NaI) system [9] it can be seen that this is the system of continuous series of solid solutions with the minimum at T = 918 K (the mole fraction of NaI is near to 0.69). The reference NaI melt is liquid at T = 973 K, whereas the melting point of NaBr is T = 1120 K and it cannot be studied at the standard temperature. Therefore, (NaBr + NaI) (0.77:0.23) system with the liquidus point of ca. T = 960 to 970 K was chosen instead of pure NaI. So, the melt sequence is as follows: NaI ? (NaBr + NaI) (0.31:0.69) ? (NaBr + NaI) (0.77:0.23).

2. Experimental 2.1. Solvent and reagents The used reagents and methods of their preparation are presented in table 1. Two mixed solvents were studied: (NaBr + NaI) (0.31:0.69) with mole fraction of NaI, xNaI ¼ 0:69 and (NaBr + NaI) (0.77:0.23) with xNaI ¼ 0:23. Each experiment required ca. 50 g of (NaBr + NaI)

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V.L. Cherginets et al. / J. Chem. Thermodynamics 91 (2015) 136–140 TABLE 1 Chemicals used in the experiments and methods of their treatment. Formula

Supplier

Purity, main substance, mass fraction

Purification method

Final mass fraction purity

Method of analysis

Ar

PASS, Ukraine

0.997

Drying over P2O5

0.998

Eu2O3 HIaq KOH NH4I NaBr NaI

Stanford materials corporation Merck Reakhim, Russia Merck Reakhim, Russia Merck

0.99999 0.57 0.999 0.998 0.995 0.999

None Distillation Drying in argon atmosphere at 600 °C None Drying under vacuum at T = 473 K Drying under vacuum at T = 473 K

0.99999 0.57 0.999 0.998 0.995 0.995

‘Baikal’ (analyser of water in gases) Zircon (analyzer of O2 in gases) Stated by supplier Density Stated by supplier Stated by supplier Stated by supplier Stated by supplier

mixture. (NaBr + NaI) (0.31:0.69) mixture was prepared by mixing NaBr and NaI taken in 0.236:0.744 mass ratio whereas for (NaBr + NaI) (0.77:0.23) system it was 0.697:0.303. Before the experiment the melts were additionally dried from oxide ion traces (admixtures of the corresponding hydroxides, carbonates and sulfates in the chemicals) by adding NH4I of reagent quality. The residual concentration of O2
in the melts was ca. (1 to 2  10
4) mol  kg
1 that was estimated on the basis of the potentiometric measurements (see below). Before the experiments the components of the salt mixtures were dried by careful heating of commercial chemicals of reagent quality in vacuum (p = 5 Pa) with slow elevation of the temperature up to 573 K. EuI2 was synthesized by dissolution of Eu2O3 in aqueous HI (extra pure), and ammonium iodide (reagent quality) taken in a molar ratio of 2:1 to Eu was added to the formed solution. The obtained solution was evaporated and dried up to the formation of a brown powder (EuI3 + NH4I with the traces of I2 and water). This powder was carefully heated in vacuum up to the beginning of I2 evaporation, which started at T = 470 K according to the following reaction

2EuI3 2EuI2 þ I2 " :

ð1Þ

At the termination of this process NH4I sublimation started, and the action of HI formed after decomposition of ammonium iodide led to an additional purification of EuI2 from oxygen-containing admixtures. To check the quality of the final product, a certain amount of the obtained EuI2 was dissolved in water acidified by acetic acid to pH = (4.7 to 5). If the precipitate or opalescence (Eu2O3) was absent, the reagent was considered as appropriate for the titration experiment. KOH (mass fraction purity 0.999) was melted in an alumina crucible, heated to T = 973 K in argon atmosphere and kept under these conditions for 1 h to provide complete removal of absorbed water. Inert atmosphere in the potentiometric cell was created using high-purity Ar (the volume fraction of the main substance was 0.9999) preliminarily dried by passing over P2O5, that provided deep purification from H2O traces. The residual concentration of oxygen in the gas did not exceed 1  10
3 volume per cent. 2.2. Calibration and titration procedures The mixture of the salts was melted in an electrochemical cell with a silver reference electrode Ag|Ag+ and an indicator one, reversible to oxide ions, Pt(O2)|YSZ where YSZ was yttria stabilized zirconia (0.9ZrO2 + 0.1Y2O3). The scheme of this cell is as follows

AgjAgþ ðmeltÞ pppp ðEu2þ Þ;

O2
ðmeltÞjYSZjO2 ðgÞjPt:

ð2Þ

The construction of the electrochemical cell is described in detail in [10]. This cell was preliminarily calibrated by the additions of certain quantities of O2
donor KOH (chemical quality). This reagent completely dissociated in molten salts according to the equation:

2OH
H2 O " þO2
:

ð3Þ

This gave the possibility to construct the dependence of emf (E, V) of cell (2) vs. the equilibrium molality of O2
(mO2
) or its index ðpO 
log mO2
Þ. These plots were used for pO calculation from the potentiometric data. Their features concerning the electrochemical behavior of Pt(O2)|YSZ electrode were discussed in detail earlier in Electrochim. Acta [11,12], so we will not dwell on them. The titration procedure was as follows. After stabilization of the temperature and emf the weight of EuI2 corresponding to a molality of ca. (0.02 to 0.04) mol  kg
1 was added to the melt (this initial molality is denoted further as m0Eu2þ ), and the equilibrium emf value was measured. The emf measurements were performed every 5 min up to the moment when three sequential values became equal. When the melt contained an excess of Eu2+ as compared with O2
the equilibrium was achieved after 30 min, in the opposite case the equilibrium state was observed after 1 h. Then a sequence of the weights of KOH (the initial molality of O2
m0O2
) was added to the melts till the initial molality of O2
became considerably greater than m0Eu2þ (from (0.05 to 0.06)

mol  kg
1, i.e., two times as much as m0Eu2þ ), and the equilibrium emf values were registered after each addition. For each experi: mental point we calculated the value of pO, the ligand number n

 ¼ ðm0 2

10
pO Þ=m0 2þ ; n Eu O

ð4Þ

corresponding to the average number of oxide ions fixed by one Eu2+ cation, the calculated values of dissociation constant K 0EuO ðpK 0EuO ¼
log K 0EuO Þ:
1  Þ  10
pO =n  =ðmol  kg
1 Þg; fK 0EuO =ðmol  kg Þg ¼ fð1
n

ð5Þ

which provides the true parameter if the solution is non-saturated with respect to EuO, and the solubility product, K 0s;EuO ðpK 0s;EuO ¼
log K 0s;EuO Þ:
2


2

 Þ  m0 2þ  10
pO =ðmol  kg Þg; fK 0s;EuO =ðmol  kg Þg ¼ fð1
n Eu 2

2

ð6Þ becomes the characteristic of the equilibrium in the case when the saturation is achieved. These parameters were estimated on the basis of the data belonging to the relevant section in the titration curve. The division of the potentiometric curves into the sections of non-saturated and saturated solutions was performed on the basis of the changes of the calculated parameters pK 0EuO and pK 0s;EuO with the increase of the titrant concentration, as described in [10]. In the non-saturated solution section, the value of pK 0EuO oscillates near a certain value, whereas pK 0s;EuO is subjected to directed shift (decrease). On the contrary, in the saturated solution section the value of pK 0s;EuO is practically constant and pK 0EuO value sequentially increases. The sets of pK 0EuO and pK 0s;EuO were used for statistical

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V.L. Cherginets et al. / J. Chem. Thermodynamics 91 (2015) 136–140

treatment according to the routine described in [13] (the accuracies are presented as standard deviations). Further the concentration equilibrium parameters will be discussed since the activity method is not developed for ‘(alkali metal halide + slightly soluble oxide)’ systems. Nevertheless, it is assumed that the deviations from the ideality have close values in all the melts.

TABLE 2
1 Results of potentiometric titration of Eu2+ cations ðm0Eu2þ ¼ 0:038 mol  kg Þ with O2
addition in (NaBr + NaI) melt with xNaI ¼ 0:23 at T = 973 K, p = 105 Paa. m0O2
=mol  kg 4.210
4 7.010
4 1.1910
3 2.7310
3 5.5410
3 1.01010
2 2.10210
2 2.78010
2 3.90410
2 4.34410
2 4.99410
2 5.70410
2 7.39110
2

3. Results and discussion The solubility of EuO in the melts was determined by the potentiometric titration of Eu2+ (EuI2) solutions with the additions of oxide ion donor that resulted in precipitation of EuO. This interaction is the reverse of the dissolution process and can be described by the following equation:

Eu2þ þ O2
EuO # :

ð7Þ

The examples of the curves of Eu2+ potentiometric titration with KOH in the studied bromide-iodide melts are shown in figure 1. They present the dependence of pO against h, which is the ratio of the initial molality of the oxide ion and the Eu2+ cation, h ¼ m0O2
=m0Eu2þ . As is seen, these dependences are similar enough one to another although the positions of the curve sections at h < 1 with respect to the ordinate axis are somewhat different. This is caused both by different values of the solubility products and by different initial concentrations of Eu2+ cations, since at high  and equation (6) can be transformed as: pO values (pO > 5) h  n

pO ¼ pK s;EuO þ logð1
hÞ þ log m0Eu2þ :

FIGURE 1. The dependence of pO vs. h at titration of Eu2+ with O2
at T = 973 K in sodium bromide–iodide melts: 1 (s) – (NaBr + NaI) (0.77:0.23), m0Eu2þ ¼
1
1 0:038mol  kg (empty), 2 (j) – (NaBr + NaI) (0.31:0.69), m0Eu2þ ¼ 0:018mol  kg ,
1 3 (+) – pure NaI [8], m0Eu2þ ¼ 0:029 mol  kg .

pO

 n

pK 0EuO =mol  kg

6.93 6.65 6.46 6.37 6.36 6.24 5.92 4.80 3.04 2.37 1.94 1.76 1.58

0.011 0.018 0.032 0.072 0.146 0.267 0.556 0.735 1.008 1.036 1.019 1.05 1.25

4.98 4.92 4.97

Average


1


2

pK 0s;EuO =mol  kg 2

7.89 7.82 7.85 7.80 7.69

4.96 ± 0.04

7.81 ± 0.08

a

Standard uncertainties of the experimental parameters are: u(p) = 3103 Pa,
1 u(T) = 3 K, uðxNaI Þ ¼ 0:005, uðm0Eu2þ Þ ¼ 0:001 mol  kg , ur ðm0O2
Þ ¼ 0:005,  Þ ¼ 0:04, uðpK 0EuO Þ ¼ 0:02, uðpK 0s;EuO Þ ¼ 0:02, uðpK EuO Þ ¼ 0:04 and u(pO) = 0.02, uðn uðpK s;EuO Þ ¼ 0:08.

TABLE 3
1 Results of potentiometric titration of Eu2+ cations ðm0Eu2þ ¼ 0:018 mol  kg Þ with O2
addition in (NaBr + NaI) melt with xNaI = 0.69 at T = 973 K, p = 105 Paa. m0O2
=mol  kg 3.12  10
4 7.17  10
4 1.19  10
3 2.77  10
3 7.26  10
3 9.68  10
3 1.75  10
2 2.01  10
2 2.38  10
2 2.77  10
2 3.37  10
2 4.78  10
2

ð8Þ

All the potentiometric curves start with a sharp decrease of pO, which testifies to the formation of unsaturated solution. The experimental values belonging to this section can be used for estimation of the dissociation constants of EuO in the melts studied using equation (5). After the sharp pO decrease, the potentiometric curves become more inclined because of precipitation of EuO (the formation of the saturated solution) and the data from the corresponding section (practically up to h = 0.7) can be used for calculating the solubility product. The examples of the experimental data treatment are presented in tables 2 and 3. The values obtained make it possible to estimate the values of pK EuO and pK s;EuO in (NaBr + NaI) (0.77:0.23) melt as (4.96 ± 0.04) and (7.81 ± 0.08), respectively. The corresponding data for other melts in question are presented in table 4. To facilitate the comparison of these values, the values obtained for pK EuO and pK s;EuO are


1

Average


1

pO

 n

pK 0EuO =mol  kg

7.24 6.95 6.83 6.60 6.31 5.99 4.06 3.76 3.18 2.64 1.79 1.55

0.018 0.041 0.068 0.159 0.415 0.554 0.995 1.140 1.223 1.353 1.000 1.102

5.51 5.56 5.60


1

5.56 ± 0.06


2

pK 0s;EuO =mol  kg 2

8.62 8.43 8.24

8.44 ± 0.16

a

Standard uncertainties of the experimental parameters are: u(p) = 3103 Pa,
1 u(T) = 3 K, uðxNaI Þ ¼ 0:005, uðm0Eu2þ Þ ¼ 0:001 mol  kg , ur ðm0O2
Þ ¼ 0:005,  Þ ¼ 0:04, uðpK 0EuO Þ ¼ 0:02, uðpK 0s;EuO Þ ¼ 0:02, uðpK EuO Þ ¼ 0:06 and u(pO) = 0.02, uðn uðpK s;EuO Þ ¼ 0:16.

also recalculated on the mole fraction scale as pK x;EuO and pK sx;EuO , respectively. Such a choice of concentration scale seems the most substantiated due to a low solubility of EuO and the recalculated values are practically referred to solubility of EuO in 1 mol of NaBr0.77I0.23, NaBr0.31I0.69 and NaI. As it will be shown below, the total concentration of non-dissociated EuO and Eu2+ in the saturated solutions does not exceed 0.0002. Hence, the mole fraction of the solvent is near 0.9998, i.e., practically equal to 1. As is seen, the rise of the iodide ion concentration results in sequential decrease of the solubility product and the dissociation constant, although in the case when the thermodynamic parameters are expressed via mole fractions the trend for the solubility products changes become less pronounced. It should be noted that the calculating errors of the obtained data increases going from (NaBr + NaI) (0.77:0.23) mixture to pure NaI melt that can be caused by increase of concentration iodide ions. The latter possess stronger reduction properties than Br
and, therefore, iodide melts are more sensitive to action of traces of O2 and H2O which are contained in the atmosphere over the melt. So, from the abovesaid it can be concluded that sequential increase of NaBr concentration in the (bromide + iodide) mixtures causes strengthening of EuO ionization in the saturated solution. This conclusion can

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V.L. Cherginets et al. / J. Chem. Thermodynamics 91 (2015) 136–140 TABLE 4 Parameters describing solubility and dissociation of EuO in melts of (NaBr + NaI) system at T = 973 K (xNaI the mole fraction of NaI in the melts), p = 105 Paa. xNaI 0.23 0.69 1 [8]

2

pfK s;EuO =mol  kg 7.81 ± 0.07 8.44 ± 0.16 8.65 ± 0.13


2

g

2


2

K s;EuO =mol  kg
8

1.55  10 3.63  10
9 2.2  10
9

pK sx;EuO

pfK EuO =mol  kg

9.70 ± 0.07 10.18 ± 0.16 10.30 ± 0.13


1

g

K EuO =mol  kg
5

1.1  10 2.8  10
6 2.0  10
6

4.96 ± 0.03 5.56 ± 0.06 5.70 ± 0.20


1

pK x;EuO 5.90 ± 0.03 6.43 ± 0.06 6.52 ± 0.20

a Standard uncertainties of the experimental parameters are: u(p) = 3103 Pa, u(T) = 3 K, uðxNaI Þ ¼ 0:005 and uncertainties reported in the table for pK EuO , pK s;EuO , pK x;EuO and pK sx;EuO are standard uncertainties.

TABLE 5 Data on concentrations of reactants of equation (7) in saturated solutions of EuO in melts of (NaBr + NaI) system at T = 973 K, p = 105 Paa. xNaI 0.23 0.69 1 [8]

log xNaI
0.638
0.161 0

sx;EuO =mol  fr

sx;Eu2þ =mol  fr


4


5

1.6  10 1.79  10
4 1.7  10
4

1.42  10 8.2  10
6 7.1  10
6

a

Rsx;EuO =mol  fr

0.081 ± 0.010 0.044 ± 0.015 040 ± 0.015

1.75  10
4 1.87  10
4 1.77  10
4

a Standard uncertainties of the experimental parameters are: u(p) = 3103 Pa, u(T) = 3 K, uðxNaI Þ ¼ 0:005, ur ðsx;EuO Þ ¼ 0:2, ur ðsx;Eu2þ Þ ¼ 0:2, ur ðRsx;EuO Þ ¼ 0:2 and the uncertainty reported in the table for a is standard uncertainty.

be confirmed by the direct solubility values (sx;EuO the concentration of non-dissociated oxide sx;Eu2þ , the concentrations of ionized form of EuO and sx;EuO , the total Eu amount in the saturated solution of EuO, a, the dissociation degree) presented in table 5. The data from this table 5 show that non-dissociated EuO is the prevailing form in all the saturated solutions of europium monoxide in the molten (bromide + iodide) mixtures. Its concentration decreases going from NaI to the most bromide-rich melt. It can be explained by the fact that dissolution of oxide without dissociation proceeds according to the so-called physical mechanism, i.e., the oxide particles become embedded in the hollow spaces in solvents which sizes are close to those of particles of non-dissociated oxide. Since the crystal radius of bromide ion is smaller than that of iodide ion in the common case we can expect a sequential decrease of a number and sizes of the available hollow spaces with the rise of bromide ion concentration. Moreover, the density for (NaBr + NaI) systems shows negligible deviations from the ideality [14]. In its turn, this causes the decrease of EuO concentration in the saturated solutions and, hence, a reduction of the total solubility. As to the parameters concerning ionization of EuO, it should be noted that the dissociation degree decreases with the rise of the iodide ion concentration in the melt although for two the most iodide-rich melts the difference is statistically insignificant. The similar conclusion can be made on the basis of the concentrations of Eu2+ in the discussed saturated solutions. The observed effect can be explained using the Pearson’s concept of hard and soft acids and bases [15]. The process of europium oxide dissociation in halide melts is accompanied with the formation of halide complexes of europium and oxo-complexes of sodium that can be expressed by the following simplified scheme:

EuO þ nX
þ mNaþ EuX n2
n þ Nam Om
2 ;

ð9Þ

where X is the halogen designation. Taking into account the fact that all the above-discussed melts contain only Na+ cations, one can assume that the formation of the oxo-complexes occurs in approximately the same extent. EuO consists of hard acid (Eu2+) and hard base (O2
), bromide ion is an intermediate base and iodide belongs to soft bases. Going from this classification, ‘hard-hard’ (Eu2 + + O2
) complex is the most stable form in saturated solutions of EuO. The formation of (Eu2+ + Br
) complexes is not so advantageous and (Eu2+ + I
) stability is the lowest in this sequence. Therefore, the addition of bromide ion to iodide melts should result in the increase of dissociation of the products formed by strong and intermediate Pearson’s acids.

4. Conclusions Within the frames of this paper, the processes accompanying the dissolution and dissociation of europium monoxide in molten (NaBr + NaI) mixtures of 0.77:0.23 and 0.31:0.69 compositions at T = 973 K are studied by potentiometric titration method using an indicator electrode reversible to oxide ions. The solubility product indices of EuO on the molality scale (pK s;EuO ) are (7.81 ± 0.08) and (8.44 ± 0.16) in melts of 0.77:0.23 and 0.31:0.69 compositions, the corresponding dissociation constant indices (pK EuO ) are (4.96 ± 0.04) and (5.56 ± 0.06), respectively. These values give us the possibility to state that non-dissociated EuO is the main form in all of the saturated solutions of EuO. The decrease of the iodide ion concentration in the melts results in the rise of EuO dissociation degree in its saturated solution. This is explained by the introduction of harder Pearson’s base (Br
) in the iodide melt that, in its turn raises the fixation degree of Eu2+ in the mixed halide complexes. As for the total solubility of EuO, it decreases going from NaI melt to the (bromide + iodide) mixtures. This is caused by the decrease of ‘physical’ solubility of non-dissociated oxide which occupies hollow spaces of available size presented in the studied ionic solvents. Some of this hollow spaces decrease with the sequential substitution of iodide ion with bromide one. Appendix A. Supplementary data Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j.jct.2015.08.001. References [1] Z. Yan, G. Gundiah, G.A. Bizarri, E.C. Samulon, S.E. Derenzo, E.D. BourretCourchesne, Nucl. Instrum. Methods Phys. Res., Sect. A 735 (2014) 83–87. [2] A.Yu. Grippa, N.V. Rebrova, T.E. Gorbacheva, V.Yu. Pedash, N.N. Kosinov, V.L. Cherginets, V.A. Tarasov, O.A. Tarasenko, Nucl. Instrum. Methods Phys. Res., Sect. A 729 (2013) 356–359. [3] R. Borade, E. Bourret-Courchesne, S. Derenzo, Nucl. Instrum. Methods Phys. Res., Sect. A 652 (2011) 260–263. [4] V.L. Cherginets, N.V. Rebrova, A.Yu. Grippa, Yu.N. Datsko, T.V. Ponomarenko, V. Yu. Pedash, N.N. Kosinov, V.A. Tarasov, O.V. Zelenskaya, I.M. Zenya, A.V. Lopin, Mater. Chem. Phys. 143 (2014) 1296–1299. [5] E.D. Bourret-Courchesne, G.A. Bizarri, R. Borade, G. Gundiah, E.C. Samulon, Z. Yan, S.E. Derenzo, J. Cryst. Growth 352 (2012) 78–83. [6] G. Gundiah, M. Gascon, G. Bizarri, S.E. Derenzo, E.D. Bourret-Courchesne, J. Lumin. 159 (2015) 274–279. [7] N.V. Shiran, A.V. Gektin, Y. Boyarintseva, S. Vasyukov, A. Boyarintsev, V. Pedash, S. Tkachenko, O. Zelenskaya, N. Kosinov, O. Kisil, L. Philippovich, IEEE Trans. Nucl. Sci. 57 (2010) 1233–1235.

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JCT 15-249