https://doi.org/10.1007/s100510050553
New considerations on the role of covalency in ferroelectric niobates and tantalates
Institut de Chimie de la Matière Condensée de Bordeaux
(ICMCB-CNRS), avenue du Dr. A. Schweitzer, 33608 Pessac, France
Corresponding author: a ville@chimsol.icmcb.u-bordeaux.fr
Received:
11
March
1998
Revised:
22
June
1998
Accepted:
16
July
1998
Published online: 15 December 1998
Values of Curie temperature, TC, and microwave relaxation frequency, fr, of
ferroelectric niobates and tantalates are found to be closely related to the
metal-oxygen network covalency. Correlations previously evidenced in perovskite-type
relaxors (PSN, PST) are confirmed here for K(Ta
Nbx)O3 (KTN)
compositions. The investigated physical characteristics, TC and fr, are
determined via dielectric measurements performed in a wide frequency range
(102–109 Hz) and as a function of temperature (250–800 K). On a theoretical
point of view, bond covalencies are evaluated through tight-binding band structure
calculations. The complex role of covalency on the metal potential is precised. Two
antagonist effects acting on both the short-range interatomic repulsions and the
rigidity and stability of the oxygen-metal network are discussed. The validity of this
approach is comforted through the example of the oxyfluoride
K3Li1.5Ta5O14.5F0.5.
PACS: 71.20.-b – Electron density of states and band structure of crystalline solids / 77.80.-e – Ferroelectricity and antiferroelectricity / 77.84.Dy – Niobates, titanates, tantalates, PZT ceramics, etc.
© EDP Sciences, Società Italiana di Fisica, Springer-Verlag, 1998
