High-temperature enthalpy of praseodymium selenides in the homogeneity range bounded by Pr sub(3)Se sub(4) and Pr sub(2)Se sub(3)

Calorimetry is used to study the enthalpy of the bounding compositions Pr sub(3)Se and Pr sub(2)Se sub(3) of the Pr sub(3-x)Se sub(4) phase (0 less than or equal to x less than or equal to 1/3) at 450-2300 K. The temperature-concentration dependences of the thermodynamic properties of Pr sub(3-x)Se sub(4) selenides in the homogeneity range are determined at 298 less than or equal to T less than or equal to 2156 K. The Pr sub(3-x)Se sub(4) enthalpy function has the following form: H(T, x) - H(298 K, x) = (2817 10 super(3) T super(-1) - 75912 + 234.6 T - 4.718 10 super(-2) T super(2)+ 2.624 10 super(-5) T super(3)) e super(-0.2086x) J/mole. An analysis of the partial enthalpies of Pr and Se shows that the chemical bonds between these elements change in simple substances and Pr sub(3-x)Se sub(4).