Using semi-empirical methods, we determined the standard heat capacity and entropy of compounds formed in the CaO-Y2O3-SiO2 system. The temperature dependences of the molar heat capacity of CaSiO3, Ca3Si2O7 calcium silicates and Y2SiO5, Y2Si2O7 yttrium silicates were calculated using the Neumann-Kopp and Kubashevsky methods.

The germanates CaGd2Ge4O12 and CaDy2Ge4O12 were synthesized from CaO, Gd2O3 (Dy2O3), and GeO2 by the standard ceramic technology. Their crystal structure was refined by X-ray diffraction analysis. The high-temperature heat capacity was measured in the temperature range 320–1000 K using differential scanning calorimetry. Their thermodynamic functions were calculated from the experimental dependences Cp = f(T).

CaTm2Ge4O12 germanate was synthesized by the solid- phase method from starting oxides. Its crystal structure has been studied using X-ray diffraction, and Its high temperature heat capacity (320-1000 K) has been determined by differential scanning calorimetry. The experimental C-p = f(T) data have been used to calculate the principal thermodynamic function.

Germanates CaYb2Ge4O12 and CaLu2Ge4O12 have been prepared via firing the solid precursor oxides CaO, Yb2O3 (Lu2O3), and GeO2 in air at 1223–1423 K. The X-ray diffraction crystal structures of the prepared germanates have been determined. The high-temperature heat capacity in the range 320–1050 K has been measured by differential scanning calorimetry (DSC). The measured heat capacities are well fitted by the Maier–Kelley equation: Cp(CaYb2Ge4O12) = ( 416.4 ± 0.40) + ( 72.67 ± 2.30)× 10^-3T - ( 50.13 ± 0.19)× 10^5T^-2 , and Cp(CaLu2Ge4O12) = ( 450.0 ± 1.75) + ( 15.46 ± 1.90)× 10^-3T - ( 78.67 ± 1.60)× 10^5T^-2 . These results have been used to calculate selected thermodynamic properties of the prepared germanates.

Orthogermanate Ca3Y2Ge3O12 has been prepared via firing solid CaCO3, Y2O3, and GeO2 in air at 1773 K. Its X-ray diffraction crystal structure has been refined (space group Ia 3̅ d, a = 12.80255(14) Å, V = 2098.34(7) Å3). The heat capacity of the prepared germanate in the range 320–1000 K has been determined by differential scanning calorimetry (DSC), and the experimental data have been used to calculate the thermodynamic properties of Ca3Y2Ge3O12.

Lithium sodium tetragermanate, LiNaGe4O9, has been prepared by solid-state reaction, by sequentially firing stoichiometric mixtures of Li2CO3, Na2CO3, and GeO2 starting materials in air in the temperature range 773–1073 K. Its unit-cell parameters have been determined by X-ray diffraction: a = 4.68007(3) Å, b = 9.3220(8) Å , c = 15.900(2) Å, and V = 694.113 Å (Z = 4, sp. gr. Pcca). The high-temperature heat capacity of the germanate has been determined using differential scanning calorimetry in the temperature range 320–1050 K. The experimental temperature-dependent heat capacity data, Cp(T), have been used to calculate the principal thermodynamic functions of LiNaGe4O9.

— The CaSm 2 Ge 3 O 10 germanate has been prepared by firing stoichiometric mixtures of CaCO 3 , Sm 2 O 3 , and GeO 2 in air in the temperature range 1423–1473 K. X-ray powder diffraction characterization with the use of the derivative difference minimization method has shown that CaSm 2 Ge 3 O 10 has a monoclinic structure (sp. gr. P 2 1 / c , 293 К) with unit-cell parameters a = 6.9779(8) Å, b = 6.92859(7) Å, c = 18.8907(2) Å, and β = 108.3280(8)°. The high-temperature heat capacity of calcium samarium germanate samples has been determined in the temperature range 320–1000 K by differential scanning calorimetry and the experimental C p ( T ) data have been used to evaluate thermodynamic properties of CaSm 2 Ge 3 O 10 .

It was established that at 298 K the molar heat capacity of alkali metal silicates K 2 O· nSiO 2 , Rb 2 O· nSiO 2 and Cs 2 O· nSiO 2 changes linearly when changing n from 1 to 4. Based on the dependencies C o p,298 =f(n), the values of the heat capacities K 2 O, Rb 2 O and Cs 2 O have been specified. Keywords: heat capacity, oxides and silicates of alkali metals.

A linear correlation has been established between the standard values of the enthalpies and the entropies of formation, the heat capacity , and the composition of oxide compounds formed in the SrO-Bi2O3, V2O5-Bi2O3, and PbO-Fe2O3 systems. The heat capacity of oxides of the SrO- Bi2O3 system was calculated using the Neumann-Kopp empirical relations, the Kumok incremental method, the Kellogg model and group contributions. It is found that the best agreement with the available experimental results is given by the Kumok method.

LiScGeO 4 and LiScSiO 4 compounds were obtained by solid-phase synthesis from Li 2 CO 3 , Sc 2 O 3 , GeO 2 (SiO 2 ). Their crystal structure has been refined using X-ray diffraction. The high-temperature heat capacity (320–1050 K) of the obtained lithium-scandium germanate and silicate was measured by differential scanning calorimetry. The thermodynamic properties were calculated based on the experimental data about heat capacity.

The paper presents data on the structure and thermodynamic properties of apatite-like lead vanadate-germanates substituted with ions of rare earth elements or bismuth. It is shown that with an increase in the ionic radius, a non-monotonic change in the parameters of the unit cell occurs. It is established that the temperature dependence of the molar heat capacity of the extremes on is observed and can be described by the equations of Mayer — Kelly and Prausnitz, Reed, Sherwood.

Обжигом на воздухе стехиометрических смесей CaCO 3 , Sm 2 O 3 и GeO 2 в интервале температур 1423–1473 K получен германат CaSm 2 Ge 3 O 10 . С использованием рентгеновской дифракции порошка методом минимизации производной разности установлено, что кристаллическая структура CaSm 2 Ge 3 O 10 (пр. гр. P 2 1 / c , 293 К) является моноклинной с параметрами элементарной ячейки a = 6.9779(8) Ǻ, b = 6.92859(7) Ǻ, c = 18.8907(2) Ǻ, β = 108.3280(8)°. Высокотемпературная теплоемкость образцов германата кальция-самария измерена в интервале температур 320–1000 К методом дифференциальной сканирующей калориметрии. Рассчитаны термодинамические свойства CaSm 2 Ge 3 O 10 на основании полученной экспериментальной зависимости C p = f ( T ).

The temperature dependence (350-1050 K) of the heat capacity of the Bi12GeO20 and Bi4Ge3O12 has been determined by differential scanning calorimetry. For these compounds and Bi2GeO5, Bi2Ge3O9, the calculation of heat capacity was carried out using the methods of Kubashevsky, Neman- Kopp and group deposits. The correlation between the specific heat capacity and the composition of the Bi2O3- GeO2 system was established.

Твердофазным синтезом из стехиометрических смесей исходных Li 2 CO 3 , Na 2 CO 3 и GeO 2 последовательным обжигом на воздухе в интервале температур 773–1073 K получен тетрагерманат лития-натрия LiNaGe 4 O 9 . С использованием рентгеновской дифракции уточнены параметры его элементарной ячейки ( a = 4.68007(3), b = 9.3220(8), c = 15.900(2) Å, V = 694.113 Å, Z = 4, пр. гр. Pcca ). Высокотемпературная теплоемкость измерена методом дифференциальной сканирующей калориметрии в интервале температур 320–1050 K. По экспериментальным значениям температурной зависимости теплоемкости C p = f ( T ) рассчитаны основные термодинамические функции LiNaGe 4 O 9 .

Erbium gallium titanate was prepared by solid-phase synthesis via the sequential calcination of precursor oxides in an air atmosphere at 1273 and 1573 K. The crystal structure of ErGaTi2O7 was characterized by full-profile analysis for the X-ray diffraction pattern of the synthesized powder sample as follows: space group Pcnb, a = 9.77326(15) Å, b = 13.5170(2) Å, c = 7.33189(11) Å, V = 918.58(3) Å3, ρ = 6.10 g/cm3. The high-temperature heat capacity of erbium gallium titanate was measured by differential scanning calorimetry within a temperature range of 320–1000 K. Based on these data, the basic thermodynamic functions of ErGaTi2O7 were calculated.

Solid solutions Bi4-xLaxTi3O12 (x=0,4; 0,8; 1,2; 1,6) were obtained by the method of solid-phase sintering. Powder x-ray diffraction determined the crystal structure of the synthesized phases. It has been found that when the La3+ ion is introduced into Bi4Ti3O12 at x ≥ 1.2, the crystal lattice changes from orthorhombic to tetragonal. Using differential scanning calorimetry, the heat capacity of the synthesized samples of bismuth-lanthanum titanates was measured in the temperature range of 350–900 K. It was found that extrema are observed on the temperature dependence of the heat capacity for Bi3.6La0.4Ti3O12 and Bi3.2La0.8Ti3O12.

It was established that at 298 K the molar heat capacity of alkali metal silicates K 2 O·nSiO 2 , Rb 2 O·nSiO 2 and Cs 2 O·nSiO 2 changes linearly when changing n from 1 to 4. Based on the dependencies C° p,298 = f(n), the values of the heat capacities K 2 O, Rb 2 O and Cs 2 O have been specified.