Displacive-type Phase Transition Research Articles

Fluorescence and phase transition of p-terphenyl crystal

The fluorescence and the excitation spectra are reported for the p-terphenyl crystal in the temperature range from 300 to 5 K. The appearance of a new band at 335 nm in the fluorescence spectrum and the large blue shift of the excitation spectrum, 1200 cm -1, on lowering the temperature are explained by the displacive-type phase transition in a wide temperature range, 191-20 K, where the dihedral angle θ of the TP molecule increases uniformly and continuously.

Unified theory of ferroelectric phase transitions: Quantum limit

In the framework of the unified theory of ferroelectrics displacive type phase transitions are investigated in theT=OK quantum limit, when the phase transition is due to the zero-point fluctuations. The critical value of the zero-point energy is evaluated in the case of the completely ordered and disordered lattices, not taking into account tunnelling.

Static and dynamic critical behaviour of displacive phase transition at Tcin 1/n expansion

Quantum effects on the static critical behaviour of an isotropic n-vector model undergoing a displacement-type phase transition are studied at Tc and to O(1/n). For Tc not=0 there is no quantum effect on eta , and for Tc=0 one gets eta =0 for d>3, and for 2<d<3 eta is due to quantum fluctuations, implying that it assumes a different value than in the classical case. The dynamical behaviour of the system violates the dynamic scaling hypothesis.

Critical dynamics and quantum effect of displacement type phase transition in 1/ n expansion

Quantum effects of critical behaviour of a displacive phase transition are studied at T c. For T c=0, η differs from the classical value. The system violates the dynamic scaling hypothesis.

Self-consistent phonon approximation and displacive phase transitions

Abstract A simple field model with a scalar order parameter and quartic anharmonic interaction is used to consider a displacive-type phase transition. It is shown that the order of the phase transition can not be determined within the framework of self-consistent phonon approximation. The considerable deviation of the temperature dependence of soft mode frequency from Curie-Weiss law far from the transition point is obtained and justified in the second-order approximation. The latter result is believed to be due to the model under consideration.