ISSN:
1600-5767
Source:
Crystallography Journals Online : IUCR Backfile Archive 1948-2001
Topics:
Geosciences
,
Physics
Notes:
The atomic coordinates of K2(NbO)2Si4O12 reported in space group P4bm satisfy the structural criteria for ferroelectricity. The estimated phase-transition temperature, Tc = 2230 (250) K, is substantially in excess of Tmelting = 1476 (5) K; the hypothetical paraelectric phase in space group P4/mbm is hence experimentally inaccessible. A strong indication that the phase transition does not occur at T 〈 Tmelting is provided by the absence of both calorimetric and dielectric permittivity anomalies below Tmelting, the linear thermal dependence of unit-cell parameters with expansion coefficients α11 = –0.53 (12) × 10–6 and α33 = 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 Ps ∼ 0.2 C m–2, provides unambiguous verification of the ferroelectric property.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1107/S0021889898016501
