Phonons, Instabilities and Origin of Polarization in KDP Crystals

G. COLIZZI; J. KOHANOFF; J. LASAVE; R L MIGONI

FERROELECTRICS

TAYLOR & FRANCIS LTD

Lugar: Londres; Año: 2010 vol. 401 p. 200 - 206

0015-0193

p, li { white-space: pre-wrap; } The gamma-phonons ofKH2PO4 (KDP) and its deuterated analogDKDPare studied via first- principles linear response calculations. The paraelectric phase shows two instabilities. One for a z-polarized mode, which leads to the spontaneous polarization Ps of the ferroelectric phase. The other corresponds to a two-fold degenerate xy-polarized mode. Other phonons are analyzed, which couple to the ferroelectric one at large amplitudes and are relevant for the ferroelectric transition.We show that Ps is mainly of electronic nature, since it arises mostly from an off-diagonal component of the Born effective charge tensor of H, with minor contribution from P atoms displacements.