T-induced displacive phase transition of end-member Pb-lawsonite

High-pressure and high-temperature transformation of Pb(II)-natrolite to Pb(II)-lawsonite.

We report on high-pressure and high-temperature chemical transformations of Pb(2+)-exchanged natrolite (Pb-NAT, Pb8Al16Si24O80·16H2O) using a combination of in situ synchrotron X-ray powder diffraction and ex situ HAADF-STEM real space imaging. Three high-pressure polymorphs of natrolites (Pb-NAT-I, II, III) are observed via step-wise pressure-induced hydrations (PIH) up to 4.5 GPa, during whic...

Molecular Dynamics Simulation of Displacive Phase Transitions

Displacive phase transitions have been extensively modelled by the 4 model. In this project, this model is applied to a system with a scalar displacement at each ‘atom’ in a three-dimensional lattice. The behaviour of the system is simulated using molecular dynamics techniques on a massively parallel computer. The code is tested to confirm that the simulation is behaving correctly and is suffic...

Pressure-induced decoupling of the order-disorder and displacive contributions to the phase transition in diguanidinium tetrachlorostannate

Theory of displacive phase transitions in minerals

A lattice-dynamical treatment of displacive phase transitions leads naturally to the softmode model, in which the phase-transition mechanism involves a phonon frequency that falls to zero at the transition temperature. The basic ideas of this approach are reviewed in relation to displacive phase transitions in silicates. A simple free-energy model is used to demonstrate that Landau theory gives...

THE ELECTRIC FIELD-INDUCED ANTIFERROELECTRIC TO FERROELECTRIC PHASE TRANSITION IN SOME (Pb,La) Zr0.55Ti0.4503 CERAMICS

Lanthanum substituted lead zirconate-titanate (PLZT) ceramics of composition 11.1/55/45 have been studied by measuring high electric field properties. Dc bias, dielectric and P-E hysteresis loop measurements have been employed to construct an E (electric field) versus T (temperature) phase diagram. At lower temperatures and small electric fields an antiferroelectric phase with tetragonal symmet...