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K 2 (NbO) 2 Si 4 O 12 : a new ferroelectric
Author(s) -
Foster M. C.,
Arbogast D. J.,
Photinos P.,
Nielson R. M.,
Abrahams S. C.
Publication year - 1999
Publication title -
journal of applied crystallography
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.429
H-Index - 162
ISSN - 1600-5767
DOI - 10.1107/s0021889898016501
Subject(s) - ferroelectricity , dielectric , natural bond orbital , phase transition , permittivity , materials science , hysteresis , space group , polarization (electrochemistry) , condensed matter physics , crystallography , analytical chemistry (journal) , x ray crystallography , chemistry , diffraction , physics , optics , computational chemistry , density functional theory , chromatography , optoelectronics
The atomic coordinates of K 2 (NbO) 2 Si 4 O 12 reported in space group P 4 bm satisfy the structural criteria for ferroelectricity. The estimated phase‐transition temperature, T c = 2230 (250) K, is substantially in excess of T melting = 1476 (5) K; the hypothetical paraelectric phase in space group P 4/ mbm is hence experimentally inaccessible. A strong indication that the phase transition does not occur at T < T melting is provided by the absence of both calorimetric and dielectric permittivity anomalies below T melting , the linear thermal dependence of unit‐cell parameters with expansion coefficients α 11 = –0.53 (12) × 10 –6 and α 33 = 24.66 (11) × 10 –6 K –1 between 5 and 843 K, and the generation of second harmonics between 300 and 1353 K. Demonstration of dielectric hysteresis under both direct and alternating current, with spontaneous polarization P s ≃ 0.2 C m –2 , provides unambiguous verification of the ferroelectric property.