Premium
Structure and Dielectric Properties of A‐Site‐Deficient Perovskite La (1− x )/3 Ag x NbO 3 (0≤ x ≤0.25) Ceramics
Author(s) -
Guo Q. H.,
Bian J. J.,
Wang L.
Publication year - 2011
Publication title -
journal of the american ceramic society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.9
H-Index - 196
eISSN - 1551-2916
pISSN - 0002-7820
DOI - 10.1111/j.1551-2916.2010.04028.x
Subject(s) - dielectric , ionic conductivity , analytical chemistry (journal) , tetragonal crystal system , dielectric loss , materials science , orthorhombic crystal system , ionic bonding , conductivity , perovskite (structure) , temperature coefficient , phase (matter) , crystal structure , vacancy defect , mineralogy , chemistry , crystallography , ion , optoelectronics , organic chemistry , electrode , chromatography , electrolyte , composite material
The crystal structure and dielectric properties of the A‐site‐deficient perovskites La (1− x )/3 Ag x NbO 3 were investigated using X‐ray diffraction (XRD), scanning electron microscopy (SEM), network analyzer, and impedance analyzer. XRD results showed that no secondary phase was observed in all samples. The crystal structure at room temperature changed from orthorhombic (0≤ x ≤0.16) via tetragonal ( x =0.20) to pseudocubic ( x =0.25) symmetry with the increase of x . The dielectric constant (ɛ r ) and temperature coefficient of resonant frequency (τ f ) of La (1− x )/3 Ag x NbO 3 ceramic increased with the increase of x due to the decrease of tilting angle of NbO 6 ‐octahedron. Whereas the quality factor ( Q × f ) decreased with increasing silver content as result of the decrease of A‐site cation/vacancy ordering. Complex impedance analysis and the dielectric properties measured at low frequency showed that the dielectric loss in La (1− x )/3 Ag x NbO 3 at low frequency was mainly caused by the silver ionic conduction, and that the composition of x =0.13 exhibited largest ionic conductivity and hence highest dielectric loss at low frequency. However, the dielectric loss originated from the ionic conductivity decreased with increasing frequency. Vacancy concentration and ionic conductivity in compounds would affect the order–disorder phase transformation for A‐site‐deficient perovskites. For the composition with higher ionic conductivity, it would undergo order–disorder phase transformation at much lower temperature. Meanwhile, the ionic conductivity or dielectric loss at low frequency increased with the increase of temperature because of the decrease in cations ordering.