Thermal behaviour of germanium bis(monohydrogenphosphate) monohydrate and characterization of derived germanium pyrophosphates

Abstract

The preparation of crystalline layered Ge(HPO₄)₂·H₂O is described and its thermal behaviour, with the phase changes observed between room temperature and 1 300 °C, reported. Three GeP₂O₇ phases can be characterized depending on temperature and heating rates. At lower temperatures (600–800 °C) a layered phase is obtained, and this then gives a monoclinic (slow heating rate) or cubic (fast heating rate) phase in the range 900–1 050 °C. The monoclinic and cubic phases then slightly decompose above 1 000 °C to give materials having P : Ge < 2 : 1. Above 1 050 °C a more drastic decomposition occurs with evolution of P₂O₅ and GeO₂. A comparison with the thermal behaviour of isostructural titanium and zirconium compounds is given.