title: The perfect soft mode: giant phonon instability in a ferroelectric.
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.
authors: Faculty of Physics, Vilnius University, Vilnius, Lithuania.
authors: R
authors: R
authors: Mackeviciute
authors: M
authors: M
authors: Ivanov
authors: J
authors: J
authors: Banys
authors: Nikola
authors: N
authors: Novak
authors: Zdravko
authors: Z
authors: Kutnjak
authors: Magdalena
authors: M
authors: Wencka
authors: J F
authors: JF
authors: Scott