Differential thermal analyses of solid-solid transitions in AgNO₃ under hydrostatic pressures to 0.7 Gpa

Abstract

Differential thermal analyses have located the transitions between low-temperature I and high-temperature II phases in AgNO₃ powder and single crystals under hydrostatic pressures ^</~0.7 GPa, with heating/cooling rates in the range 0.1-1.5 K s^-1. Isobaric transition temperatures plot linearly against heating/cooling rates and, extrapolated to zero rate, show hystereses between I → II and II → I transition temperatures which are comparable with the 'regions of indifference' of Bridgman's isothermal experiments. The present results suggest an initial slope of -0.090 μK Pa^-1 and zero initial curvature for the I-II phase boundary. Greater hystereses are observed for the I-II transitions near intersection with the II-II' λ transition at ^</~0.7 GPa. An improved, quantitative description is achieved for the Kennedy-Schultz data on the linear growth rates of II,II? → I at 0.1 MPa. For II' (with ordered NO₃^- ions) → I the growth rates show temperature dependence markedly different than growth rates for II(with disordered NO₃^-) → 1 and I → II.