The molar heat capacity of the Lu2O3 ⋅ 2HfO2 solid solution has been determined at 4.5–347 K, and its thermodynamic functions have been calculated in the range 0–1300 K.

The first measurements are made of the isobaric heat capacity of single-phase pyrochlore ytterbium titanate synthesized and studied via XRD, SEM, and EDX in the 2–1869 K range of temperatures. A magnetic transformation at <20 K and a lack of structural transformations throughout the region of Yb2Ti2O7 are confirmed. Thermodynamic functions (entropy, the increment of enthalpy, and the Gibbs free energy of the formation of Yb2Ti2O7 from elements and binary oxides at 298.15 K) are calculated, and the contribution to the heat capacity of the Schottky anomaly is evaluated.

Heat capacity of single-phase samarium-magnesium hexaaluminate SmMgAl11O19 was measured by relaxation, adiabatic and differential scanning calorimetry in the region 2–1864 K. Thermodynamic functions were calculated based on the smoothed values of heat capacity. Possible inaccuracies in the assessment of heat capacity and entropy using the Neumann–Kopp rule in the field of low and high temperatures are shown.

The molar heat capacity of the solid solution Tm2O3‧2HfO2 has been determined for the first time by relaxation, adiabatic and differential scanning calorimetry, the temperature dependences of entropy and enthalpy increment in the temperature region 0–1800 K have been calculated, and the contribution to the heat capacity of the Schottky anomaly at 0–300 K has been evaluated.

The molar heat capacity of the solid solution Tm2O3‧2HfO2 has been determined for the first time by relaxation, adiabatic and differential scanning calorimetry, the temperature dependences of entropy and enthalpy increment in the temperature region 0–1800 K have been calculated, and the contribution to the heat capacity of the Schottky anomaly at 0–300 K has been evaluated.

The heat capacity of LaMgAl11O19 with a magnetoplumbite structure was measured in the temperature range of 7–1865 K using relaxation, adiabatic, and differential scanning calorimetries. The obtained temperature dependences of the heat capacity are consistent based on adiabatic calorimetry data. Thermodynamic functions (entropy, enthalpy change, and reduced Gibbs energy) in the range 0–1865 K were calculated from fitted values. By using high-temperature X-ray diffraction, thermal expansion in the range of 300–1200 K was studied and the coefficient of thermal expansion of LaMgAl11O19 was calculated.

The temperature stages of crystallization process for thulium titanate of pyrochlore structural type during the heating of hydroxide precursor obtained by reverse precipitation have been studied by DSC/TG, XRD, and electron microscopy. Tm2Ti2O7 has been measured in the temperature range 2–1870 K and thermodynamic functions at 0–1900 K and the Gibbs energy of formation from oxides and elements have been calculated based on smoothed heat capacity. The contribution of the Schottky anomaly at 20–320 K into heat capacity has been revealed.

Изобарная теплоемкость образца твердого раствора ЕГ2О3∙2HfOi, охарактеризованного методами РФА, электронной микроскопии и химического анализа, измерена методами релаксационной, адиабатической и дифференциальной сканирующей калориметрии в интервале 2.4–1807 K; рассчитаны термодинамические функции. Определен вклад аномалии Шоттки в области 2.4–300 K.

The isobaric heat capacity of pyrochlore gadolinium titanate Gd2Ti2O7 is measured in the 2–1825 K range of temperatures. Thermodynamic functions (entropy, enthalpy change, reduced Gibbs energy) are calculated using consistent smoothed values of heat capacity. The Gibbs energy of the formation of Gd2Ti2O7 from oxides in the high temperature range is estimated.

Erbium titanate was synthesized by the coprecipitation of erbium and titanium hydroxides followed by high-temperature annealing. The temperature intervals of the formation sequence of the pyrochlore-type crystal structure were determined. The isobaric heat capacity of erbium titanate in the range 2–1870 K was measured by relaxation calorimetry, adiabatic calorimetry, and differential scanning calorimetry. The smoothed heat capacity values were used to calculate the entropy and enthalpy increment in the range 0–1900 K, evaluate the contribution of the Schottky anomaly at temperatures up to 300 K, and calculate the Gibbs free energy of erbium titanate formation at 298.15 K.

Pyrochlore-type neodymium and gadolinium zirconate hafnates have been prepared and identified. The heat capacities of the prepared samples have been measured by differential scanning calorimetry in the range 310–1800 K. Temperature-dependent cubic unit cell parameters have been determined and thermal expansion coefficients assessed in the range 298–1273 K using high-temperature X-ray diffraction. The thermal diffusivity of the samples was measured by the laser flash method, and the temperature-dependent thermal conductivity was calculated taking into account the porosity of the samples.

The synthesis and identification of lanthanum and samarium zirconate–hafnates of the pyrochlore structure type have been reported. The heat capacity of the samples in the temperature range 310–1380 K was measured by the differential scanning calorimetry method. The temperature dependences of the cubic lattice parameters were determined, and the thermal expansion coefficients were evaluated in the range 298–1273 K using high-temperature X-ray powder diffraction. The thermal diffusivity of the samples was measured by the laser flash method, and the temperature dependences of the thermal conductivity were calculated considering the porosity of the samples.

Isobaric heat capacity measurements in the range 2.4–1807 K have been performed by relaxation calorimetry, adiabatic calorimetry, and differential scanning calorimetry on a Ho2O3‧2HfO2 solid solution sample prepared and characterized by X-ray powder diffraction, electron microscopy, and chemical analysis, and thermodynamic functions have been calculated. The Schottky anomaly contribution has been determined in the range 2.4–300 K.

The molar heat capacity of Sm 3 TaO 7 was determined by relaxation, adiabatic and differential scanning calorimetry in the region of 2–1350 K and the thermodynamic functions were calculated. The total contribution of the Schottky anomaly to the heat capacities of samarium tantalate was evaluated. The temperature dependences of the parameters of the orthorhombic crystal lattice of the space group C 222 1 in the temperature range of 300–1204 K have been determined and the coefficients of thermal expansion have been estimated. The temperature dependence of heat capacity of samarium tantalate exhibits an anomaly in the region of 1116–1275 K associated with the structural phase transition. The space group of the high-temperature orthorhombic phase Sm 3 TaO 7 is identified as Cmcm .

The processes occurring during heating of a stoichiometric mixture of lanthanum, samarium, magnesium, and aluminum hydroxides synthesized by the reverse precipitation method have been studied by DTA/TG and X-ray powder diffraction methods. The conditions for the synthesis of single-phase LaMgAl11O19 and SmMgAl11O19 samples of the magnetoplumbite structure type have been determined, and the isobaric heat capacity has been measured in the temperature range 317–1817 K, showing the absence of structural transformations in this range.

The processes occurring during heating of a stoichiometric mixture of lanthanum, samarium, magnesium, and aluminum hydroxides synthesized by the reverse precipitation method have been studied by DTA/TG and X-ray powder diffraction methods. The conditions for the synthesis of single-phase LaMgAl 11 O 19 and SmMgAl 11 O 19 samples of the magnetoplumbite structure type have been determined, and the isobaric heat capacity has been measured in the temperature range 317–1817 K, showing the absence of structural transformations in this range.

Results are presented from measuring the molar heat capacity of the Dy 2 O 3 ‧2HfO 2 solid solution in the range of 2.5–346 K. The entropy, enthalpy increment, and reduced Gibbs energy at T = 2.5–1350 K are calculated according to literature data. The general form of the Schottky anomaly is determined.

The molar heat capacity of praseodymium hafnate with the pyrochlore structure in the temperature range 2.4–345.6 K was measured by relaxation and adiabatic calorimetry. The thermodynamic functions of Pr2Hf2O7 were calculated, and the anomalous entropy in the range 0–20 K was estimated. The general form of the anomalous heat capacity at 20–300 K was determined.

Relaxation, adiabatic, and differential scanning calorimetry in the 2–1350 K range of temperatures are used to measure the molar heat capacity of synthesized gadolinium tantalate Gd 3 TaO 7 characterized via X-ray diffraction, scanning electron microscopy (SEM), and chemical analysis. Such thermodynamic functions of the sample as entropy, the change in enthalpy, and reduced Gibbs energy are calculated. The enthalpy of formation of Gd 3 TaO 7 from elements is determined from literature data. Gadolinium tantalate’s Gibbs energy of formation from oxides in the range of high temperatures is calculated to estimate the stability of gadolinium tantalate relative to its constituent oxides.

The molar heat capacity of europium hafnate at low temperatures (4–345 K) was determined for the first time. The contribution of the Schottky anomaly to the heat capacity was estimated and thermodynamic functions in the range of 0–1300 K were calculated.