Dielectric and Structural Characteristics of Ba- and Sr-based Complex Perovskites as a Function of Tolerance Factor

Abstract

The temperature coefficient of the dielectric permittivity (τ ε ) of nonferroelectric complex perovskites is of importance in the application of these cermaics to microwave filters and resonators. Recent work has directly related changes in the τ ε of complex perovskites to the onset of structural phase transitions which involve tilting of the octahedra. It can be argued that the onset of octahedral tilting is controlled by the tolerance factor (t). Thus, a relationship between τ ε and t is postulated. This relationship is discussed and transmission electron microscopy is used to demonstrate examples of the structural modifications which cause the anomalies in τ ε at given values of t.

The influence of Mn substitution on the local structure of Na0.5Bi0.5TiO3 crystals: Increased ferroelectric ordering and coexisting octahedral tilts

“…21,[64][65][66][67][68][69] In NBT, following theoretical 21 and experimental studies, 68,69 it is believed that oxygen octahedral tilting is the dominate source of the intensity. 32,70 Evidence of in-phase octahedral tilting in Mn-NBT at room temperature was apparent in (001) SAED patterns by weak 1/2 (ooe) superlattice reflections, as marked by an arrow in Fig. 5(a).…”

“…Compounds in the perovskite family are found to exist over the tolerance factor range 1.05 > t > 0.78. 70 An in-phase tilting distortion generally has a smaller value of t than antiphase ones. It is known that Mn substitution is incorporated onto the A sites and that the ionic radius of Mn 3þ (0.65 Å ) is significantly smaller than Bi 3þ (1.28 Å ) or Na þ (1.39 Å ): this could decrease the value of t and, accordingly, suppress anti-phase rotations, producing slightly more intense 1/2 (ooe) reflections.…”

A Crystal-Chemical Framework for Relaxor versus Normal Ferroelectric Behavior in Tetragonal Tungsten Bronzes

“…The average (A1+A2)/2 ionic radius is a metric which influences the O-B-O bond length similar to the effect of Ba/Sr ratio in BST perovskite-structured ceramics. 38 The A1 tolerance factor is related to the driving force for octahedral tilting in a manner similar to that described for Ba-and Sr-based complex perovskites by Reaney et al 47 Low A1 tolerance factors generally occur for compositions with small A1 site ions which also decrease the average (A1+A2)/2 ionic radius. Hence, these two metrics are co-dependent but each relates to a different crystal-chemical mechanism for stabilizing ferroelectricity.…”

Microstructural origin for the piezoelectricity evolution in (K0.5Na0.5)NbO3-based lead-free ceramics

“…At 25 C, this monoclinic phase is stable in the composition range of 0.25 < x < 0.40. However, according to Glazer 38 and Reaney et al, 33,39 the b þ in-phase tilting should produce 1/2{oeo} superlattice spots with h 6 ¼ l (h and l are the two odd Miller indices). This implies that they should be absent in the h110i zone-axis electron diffraction patterns.…”