Thorium monophosphide ThP cr

ThP(cr) has the fee NaCl stracture, isomorphous with most of the lower actinide MX(cr) compounds, (X = N, S, P). It was initially thought to have a considerable range of homogeneity [1965GIN/WIL], but in a detailed study of the Th-ThP subsystem, Javorsky and Benz [1967JAV/BEN] showed that the lower phase boundary is at ca. ThPo.98 over most of its range of stability. The upper phase boimdaiy has still not been established. 

Maurice et al. [1979MAU/BOU] have measured the heat capacity of ThP(cr) from 2 to 15 K, but there are no other heat capacity data above this temperature. Rand [1975RAN] estimated the entropy of ThP(cr) by a comparison of the entropies of thorium and uranium compounds of nitrogen, sulphur and phosphoras, as 5 ° (ThP, cr, 298.15 K) = (70.3 + 4.2) J-K -mol. The corresponding enthalpy of formation was calculated by the same author from the combined measurements of the emf study by [1966GIN/ARO] and the mass spectrometric study by [1963GIN/EFI] as (ThP, cr, 298.15 K) = (347 + 42) kJ-mol. As noted below and in Appendix A, there are some doubts about the validity of the data obtained in the latter study, and these values are given for information only. 

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