Details

Autor(en) / Beteiligte

• Kadlec, Filip
• Nuzhnyy, Dmitry
• Kadlec, Christelle
• Petzelt, Jan
• Savinov, Maxim
• Kamba, Stanislav

Titel

Unusual features of lattice dynamics in lawsonite near its phase transitions

Ist Teil von

• Scientific reports, 2022-04, Vol.12 (1), p.6157-6157, Article 6157

Ort / Verlag

England: Nature Publishing Group

Erscheinungsjahr

2022

Link zum Volltext

Quelle

EZB Free E-Journals

Beschreibungen/Notizen

• 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 [Formula: see text] 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 [Formula: see text] and a ferroelectric one, occurring at [Formula: see text]. The former one is accompanied by a flat maximum in the THz-range permittivity [Formula: see text] near [Formula: see text], which is due to an overdamped polar excitation in the [Formula: see text] spectra reflecting the dynamics of water and hydroxyl groups. The strength of this mode decreases on cooling below [Formula: see text], and the mode vanishes below [Formula: see text] due to hydrogen ordering. At the pseudoproper ferroelectric phase transition, two independent anomalies in permittivity were observed. First, [Formula: see text] exhibits a peak at [Formula: see text] due to critical slowing down of a relaxation in the GHz range. Second, infrared and THz spectra revealed an optical phonon softening towards [Formula: see text] which causes a smaller but pronounced maximum in [Formula: see text]. Such anomaly, consisting in a soft mode polarized perpendicularly to the ferroelectric axis, is unusual in ferroelectrics.