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8Journalof Siberian Federal University. Chemistry 1 (2012 5) 37-40
y^K 536.63
Thermal Expansion of Lead Germanate Glass
Liliya А. Irtyugo, Liubov T. Denisova, Victor ]VL Denis ov*, Natalia V. Belousova and Alexauder S. Samoilo
Siberian Federal University 79 Svobodny, Krasnoyarsk, 660041 Russia 1
Received 2.03.2012, received in revised form 9.03.2012, accepted 16.03.2012
The thermal expansion of lead germanate glass has been measured in the temperature range 310-583 K. It was established that the absolute value of the coefficient of thermal expansion increases as the temperature rises to 400 K and then it is practically held constant.
Keywords: thermal expansion, glass, lead germanate.
Introduction
Oxide compounds formed in the GeO2-PbO system is of practical importance in view of their valuable properties and for a long time attracts considerable attention of scientists [1-3]. By now there are many works devoted to study of ferroelectric and other electrophyfical properties of relevant materials. Though, their thermodynamic and thermal physical properties have not been adequately explored. The aim of this work is to investigate the thermal expansion ofPbGeO3 glass.
Results and discussion
The thermal expansion of PbGeO3 glass was measured by the procedure described in [4, 5]. A DIL 402 C (NETZSCH) dilatometer was used for experiments. The measuring error amounted to 3 %. According to [6], the coefficient of thermal expansionaT is determined by the equation
a - 1
T ( I M- I ' (1)
LT VdT ) p
where LT is the length of sample at given temperature. When the extension of samples is recorded in a relatively small temperature range, the thermal expansion of homogeneous itotropic materials is noted to be characterized by the mean coefficient of linear thermal expansion:
* Corresponding author E-mail address: [email protected]
1 © Siberian Federal University. All rights reserved
L - L
_ ^t ^o Lto (-To)
^^ tt — t \ • (2)
That there were complications of obtaining compounds of GeO2-PbO system was indicated in [3, 7, 8]. In the present work; the synthesis and the control of PbGeO3 samples were conducted as in [9]. The obtained PbGeO3 glass is shown in Fig 1.
Figure 2 gives data onthermal expansion of PbGeO3 glasses.
The upper limit of measurements was bounded by the temperature 583 K beginning from which a change of behavior of the dLIL0 curve took place. The decelerating monotonic rise of the relative length extension of the PbGeO3 sample occurs at 583-630 K. As the temperature increases > 630 K, a decreasing dLIL0 (not shown in Fig. 2) is observed. We connect this phenomenon with the softening of the glass [9]. In studies of the temperature dependences of the heat capacity of these glasses at T > 630 K, an anomalous growth of Cp associated also with the softening of glass was found [9].
The thermal conductivity of the PbGeO3 glass has been measured in [10] to these temperatures
only.
Kinetics of devitrification of PbGeO3 has been studied comprehensively by C. Tomasi et al. [11]. It was established that the DSC curves of this glass at heating rate of 10 KImin were characterized by extremes at 643, 703 and 843 K. The change of heating rates from 0.1 K/min to 50 K/min resulted in shifts of the peaks to the range of higher temperatures. The first peak was related to the crystallization limit aLd second one to the "metastablelstable state" transition [11].
Based on the dL/Lo = f(T) dependence, we obtained the temperature dependence of the coefficient of thermal expansion of PbGeO3. The -values of a was determined to increase as the temperature rises from 310 K to 400 K and then they are practically held constant, equal to ~ 10-10"6 K-1.
Accordingly to [10], PtGeO3 glasses enhibit lows values tf the tnermal conductivity find their weak dependence on tire femperature. ft crn point to the ptesence of r structural regularity and other center; of phonoh rcattering. It can be cohnected with the complications tf obtaining lead-aonfaining oxide compounhsthrough a partial volatilization oW PbO. Besides, PbO is characterized
Fig. 1. Image of PbGeO3 glass
Fig. 2. Influence ofthe temperature on the relative length extension (dLIL0) of the PbGeO3 glass
by a positional disorder of crystal lattice [12]. The fact is that it crystallizes in the lattice identical to CaF2 [13]: the lead occupies positions of the calcium and the oxygen takes up positions of the fluorine. In this case rhe captcity of vacant sites for the oxygen is two times larger than there are oxygen atoms in the lattice. There are two modeficytions ofPbO [14]: tetragonae (low-temperature) and orthorhombic (high-temperature) ones. Within one crystal type, they can be characterized by various symmetry groups as a result of alternative positions of oxygen atoms with the invariant sublattice ou lea..
It may be suggested thae the nforesaid conditions the eehaviof of the PbGeO3 glatses ft high temperatures.
Referencas
1. Denisov V.M., Zhereb V.P., Denisova L.T., El'bergM.S., Storozhenko V.A. Stable and metastablf phase equilibria in the liquid-state and solid-state PbO-GeO2 system. Inorganic Materials. 2001. V. 47. № 13. pp. 1428-1449.
2. Bush A.A., Venevtsev Yu.N. Monokristally s segnetoelektricheskimi i svyazannymi svoistvami v sisteme PbO.GeO2 i vozmozhtye oblasti ikh primenyntya (Single crystals with ferroelectric and re.ated propertier in tie PaO-GeO2 system and potenteal fields of theie ppplication). Moscow: NIITEKHIM, 1981. 70 p.
3. Duda V.M., Baranov A.I., Ermakov A.S., Slade R.C.T. Influence of the Defect Structure on the Electrical Conductivity of Pb5Ge3On Single Crystals at High Temperatures. Phys. Solid State. 2006. V. 4t. № 1. pp. 59-63.
4. Denisov V. M., Denisora L. T., Irtyugo L. A. attd Baront V. it. Thtrmal physical properties oe Bi4Ge3On stngle crysMs.geys. Soeid State. 2010. V. 52!. № 7. pp. e362-1365.
5. Denisov V. M., Irtyugo L. A., Denisova L. T. and Ivanov V. V. Thermophysical properties of Bg2GeO20 singte crystals. High Temp. 20t0. V. 48. № 5. p(. 75e-755.
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11. Tomasi C., Scavini M., Speghini A., Bettineli M., Riccardi M.P. Devetrication kinetics of PbGeO3 isothermal and nonisothermal study. J. Thermal. Anal. Calorim. 2002. V. 70. pp. 151-164.
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13. Narai-Sabo I. Inorganic crystal chemistry. Budapest. Pub. of Hungary SA. 1969. 504 p.
14. Kovtunenko P.V. Fizicheskaya khimiya tverdogo tela. Kristally s defektami (Physical chemistry of solids. Crystals with defects). Moscow: Vysshaya shkola, 1993. 352 p.
Термическое расширение свинцово-германатного стекла
Л.А. Иртюго, Л.Т. Денисова, В. М. Денисов, Н.В. Белоусова, А.С. Самойло
Сибирский федеральный университет, Россия 660041, Красноярск, пр. Свободный, 79
Измерено термическое расширение свинцово-германатного стекла в интервале температур 310-583 К. Установлено, что значение коэффициента термического расширения растет по абсолютной величине с увеличением температуры в интервале 310-400 К.
Ключевые слова: термическое расширение, стекло, германат свинца.
