Low-temperature elastic anomalies in CaTiO₃: dynamical characterization

Abstract

Pulse-echo ultrasonic measurements of elastic coefficients of CaTiO(3) show anomalous behavior around 200 K, with a notable rise in the attenuation coefficient. Molecular dynamics simulation is used to simulate the elastic response of a mono-domain (MDm) and a poly-domain (PDm) configuration of CaTiO(3) using the Vashishta-Raman interatomic potential. The PDm is obtained by cooling the melt from 3600 to 300 K at a rate of 0.5 K ps(-1), so that it recrystallizes to the PDm orthorhombic configuration. The elastic behavior is simulated in the temperature range from 300 to 20 K. In the MDm, it is observed that the bulk modulus varies linearly with temperature, while in the PDm an anomalous hardening is seen around 210 K. The bulk modulus of the PDm fluctuates strongly and is lower than that of the MDm. Neither the pair correlation function nor the Ti-Ti-O bonding angle indicate a true structural phase transition in this range of temperatures. Given the absence of any apparent change in the structure, a possible explanation for this phenomenon is the emergence of a certain class of dynamical instability associated with domain wall motion. Curiously, the pressure fluctuations in both the MDm and PDm configurations follow a power law distribution f ~ P(-α), with the exponent independent of applied strain and temperature. Time series for pressure are used to analyze the dynamics by time-delay reconstruction techniques. The calculus of embedding and correlation dimension indicates that in the polycrystalline configuration, low-dimension dynamics (<26) appears, which tend to disappear at higher temperatures.

Control of surface potential at polar domain walls in a nonpolar oxide

“…The squared frequency decreases almost linearly with increasing temperature. The elastic losses are low between 10 K and 100 K but show a rapid increase above 100 K. This is consistent with the behavior observed previously by resonant ultrasound spectroscopy in CTO 34 and pulse-echo ultrasonic technique 35 . The RPS response with respect to the electric field is linear and we can therefore exclude electrostriction, which would have a quadratic dependence.…”

Structural and dynamic properties of vitreous and crystalline barium disilicate: molecular dynamics simulation and Raman scattering experiments

“…The same functional form of the effective interaction potential has been used to describe several other materials, such as super ionic conductors [12,13], oxides [14][15][16], and perovskites [17,18].…”

An interaction potential for barium sulfide: A molecular dynamics study

“…The same functional form of the effective interaction potential has been used to describe several other materials, such as super ionic conductors [24,25], oxides [26][27][28], and perovskites [29,30]. Based on previous simulations [26], the exponents in the steric repulsion term were chosen to be 11, 9, and 7 for Ba-Ba, Ba-S and S-S interactions, respectively.…”