Unusual features of lattice dynamics in lawsonite near its phase transitions

0557601 - FZÚ 2023 RIV GB eng J - Journal Article
Kadlec, Filip - Nuzhnyy, Dmitry - Kadlec, Christelle - Petzelt, Jan - Savinov, Maxim - Kamba, Stanislav
Unusual features of lattice dynamics in lawsonite near its phase transitions.
Scientific Reports. Roč. 12, č. 1 (2022), č. článku 6157. ISSN 2045-2322. E-ISSN 2045-2322
R&D Projects: GA ČR(CZ) GA20-01527S
Institutional support: RVO:68378271
Keywords : lawsonite * phase transitions * dielectric spectroscopy
OECD category: Condensed matter physics (including formerly solid state physics, supercond.)
Impact factor: 4.6, year: 2022
Method of publishing: Open access

Lattice dynamics of a single crystal of lawsonite were studied over a broad range of frequencies (1 Hz to 20 THz) using impedance, THz time-domain and infrared spectroscopies. Based on polarized spectra of complex permittivity ε̂ measured as a function of temperature between 10 K and 500 K, we analyzed the properties of the two known phase transitions—an antiferrodistortive one near Tc1 = 270 K and a ferroelectric one, occurring at Tc2 = 124 K. At the pseudoproper ferroelectric phase transition, two independent anomalies in permittivity were observed. First, ε̂a exhibits a peak at Tc2 = 124 K due to critical slowing down of a relaxation in the GHz range. Second, infrared and THz spectra revealed an optical phonon softening towards Tc2 which causes a smaller but pronounced maximum in ε̂b. Such anomaly, consisting in a soft mode polarized perpendicularly to the ferroelectric axis, is unusual in ferroelectrics.
Permanent Link: https://hdl.handle.net/11104/0333381