Understanding Solid-State Phase-Formation Processes by Using the High-Temperature Gas Balance: The Example of Zr2PTe2

Inorganic solid-state synthesis with phosphorus and tellurium requires a careful control of the reaction parameters because of the high volatility of the components. This initial disadvantage can be used as a benefit for the investigation of phase-formation mechanisms by analyzing the individual vapor pressure behavior. The high-temperature gas balance is introduced as a device for detection of heterogeneous solid-gas equilibria in closed reaction systems. The experimentally challenging synthesis of the phosphide telluride Zr2PTe2 is examined as a model system: optimized synthesis runs at lower temperatures (upsilon = 650 degrees C) in a faster time, while the quantity as well as the crystalline powder quality is increased. A stepwise solid-solid reaction of zirconium and tellurium according to Ostwald's rule of stages and the shrinking core model is revealed while phosphorus sublimes and subsequently condenses to react to the ternary compound. Additional phenomena such as melting, expansion, and mechanical instabilities can be observed that broaden the possibilities of the gas balance.