BINARY TETRAPHOSPHATES M (NH₄)₂P₄O₁₃ (M=Si, Ge, Sn, or Ti): SYNTHESIS IN THE AMMONIUM POLYPHOSPHATE MELT AND THERMAL BEHAVIOUR

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Reactions of MO₂·nH₂O (M=Si, Ge, Sn, Ti, Zr, or Hf) with NH₄PO₃ have been studied in the 200-400°C range. Conditions of formation for tetraphosphates M(NH₄)₂P₄O₁₃ (M=Si, Ge, Sn, or Ti) have been elaborated. XRD studies have been performed for powder Ti(NH₄)₂P₄O₁₃ [triclinic, space group P1, with a=15.03 (1), b=7.933 (1), c=5.079 (2) Å; α=99.15 (3), β=97.05 (3), γ=83.41 (3)°] and Sn(NH₄)₂P₄O₁₃ [triclinic, space group P1, with a=15.15(1), b=8.010 (4), c=5.107 (7) Å; α=99.90 (2), β=96.82 (3), γ=83.87 (7)°]. Thermal behaviour of the tetraphosphates has been investigated in the 20-1000°C range.