1. The perfect soft mode: giant phonon instability in a ferroelectric
- Author
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Zdravko Kutnjak, James F. Scott, R. Mackeviciute, Magdalena Wencka, Nikola Novak, Juras Banys, and Maksim Ivanov
- Subjects
Phase transition ,Waveguide (electromagnetism) ,Domain wall (magnetism) ,Materials science ,Condensed matter physics ,Phonon ,Orders of magnitude (temperature) ,General Materials Science ,Soft modes ,Coaxial ,Condensed Matter Physics ,Ferroelectricity - Abstract
Previous studies of unstable ('soft') optical modes in ferroelectrics have reported minimum frequencies of 1 cm(-1) (30 GHz) for underdamped phonons. In this work we fabricate a cylindrical coaxial specimen and rectangular plate waveguide specimens of tris-sarcosine calcium chloride (TSCC) and follow its soft mode several orders of magnitude lower to 1 GHz. Below 30 GHz the relaxation time is probably characteristic of domain wall motion; the new theory of Pakhomov et al (2013 Ferroelectrics at press) predicts 0.5 THz far from TC and a (T - T(C))/T(C) dependence, in agreement with our experimental values. This discovery has implications for GHz electronics such as phased array radar or other voltage-tunable low-loss components. The mean-field frequency description of the soft mode response f(T) is supported via precision calorimetry on TSCC with and without Br-doping. The ferroelectric-antiferroelectric phase transition, previously suggested from high-pressure data, is confirmed at 45 K at 1 atm.
- Published
- 2013
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