Thermodynamic properties of bismuth tellurites Bi₂TeO₅, Bi₂Te₄O₁₁, Bi₁₀Te₂O₁₉ and Bi₁₆Te₅O₃₄

Abstract

The increasing importance and practical implementations of bismuth tellurites Bi₂TeO₅, Bi₂Te₄O₁₁, Bi₁₀Te₂O₁₉ and Bi₁₆Te₅O₃₄ require sound knowledge on their thermodynamic properties like specific molar heat capacity (C _p,m), enthalpy ($\Delta_{{{\text{T}}^{\prime } }}^{\text{T}} H_{\text{m}}^{0}$), entropy ($\Delta_{{{\text{T}}^{\prime } }}^{\text{T}} S_{\text{m}}^{0}$) and Gibbs energy ($- \Delta_{{{\text{T}}^{\prime } }}^{\text{T}} G_{\text{m}}^{0}$). The specific molar heat capacities of the tellurites synthesized were measured experimentally, and their dependence on temperature was determined by the least squares method. The coefficients a, b and c in the equation:

$$C_{\text{p}} = a + b \cdot T - c \cdot T^{ - 2}$$

were determined. The relative error between the experimentally determined specific molar heat capacity and the one calculated by the equation was found to be in the range 0.41–1.39 %. The coefficient of correlation (R) was close to unity for all the tellurites studied which indicated that the calculation method is adequate. The specific molar heat capacity (C _p,m), enthalpy ($\Delta_{{{\text{T}}^{\prime } }}^{\text{T}} H_{\text{m}}^{0}$), entropy ($\Delta_{{{\text{T}}^{\prime } }}^{\text{T}} S_{\text{m}}^{0}$) and Gibbs energy ($- \Delta_{{{\text{T}}^{\prime } }}^{\text{T}} G_{\text{m}}^{0}$) were calculated.