The Thermochemical Behaviour of Te₈O₁₀(PO₄)₄ and its Use for Phosphide Telluride Synthesis 

Abstract

The tellurium oxide phosphate Te 8 O 10 (PO 4 ) 4 was synthesised by thermal decomposition of Te 2 O 3 HPO 4 at temperatures above 400°C. Te 8 O 10 (PO 4 ) 4 melts at 570°C and evaporates at 820°C. The thermodynamic standard data were determined by solution calorimetry and differential scanning calorimetry and were optimised by thermodynamic model- IntroductionA quite large number of metal pnictide chalcogenides have so far been described as antimonide selenides [1-5], antimonide tellurides [4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19], arsenide selenides [4,[18][19][20][21][22][23][24][25][26][27][28][29][30][31], arsenide tellurides [18,[30][31][32][33][34][35][36][37], and even phosphide sulfides [6, 18,29,[38][39][40][41][42] and phosphide selenides [4, 18,23,[40][41][42]. On the other hand, ternary phosphide tellurides seem to be extraordinary compounds, as only a small number of those are known by now. Some of them consist of isolated phosphide and telluride anions: the uranium phosphide telluride UPTe [43] and the recently found compounds Ti 2 PTe 2 [44, 45], Zr 2 PTe 2 [46] and Ce 3 Te 4-x P x [47]. Beside these compounds, other phosphorus and tellurium containing compounds are described: The telluro-phosphides IrPTe [48], OsPTe [49] and RuPTe [49], which consist of M 3+ cations besides [P-Te] 3dumbbells, and the compound BaP 4 Te 2 [50] build from Ba 2+ cations and 1 ∞ [P 4 Te 2 ] 2anions. On the other hand, in the cationic clathrate Si 46-2x P 2x Te x [51,52] the framework is built from 4-bonded silicon and phosphorus atoms, the cages are filled with tellurium atoms. As the smaller cages in type I clathrate structures are often only filled partially with tellurium, the compound exhibits a phase width.Remarkably, no binary phosphorus-tellurium compounds are known, which additionally reflects the low affinity of the two elements to each other. Therefore, the synthesis of compounds that contain phosphorus and tellurium is quite challenging and 2153 ling of the binary system TeO 2 /P 2 O 5 : ∆H 0 298 [Te 8 O 10 (PO 4 ) 4 ] = -5844(2) kJ·mol -1 ; S 0 298 [Te 8 O 10 (PO 4 ) 4 ] = 823.3 J·mol -1 ·K -1 . The phase relations in quaternary systems M/P/Te/O (M = Ti, Zr, Ce) were calculated and optimised synthesis parameters for phosphide tellurides were derived.