Structure of strontium barium niobate Sr _x Ba_1 − x Nb₂O₆ (SBN) in the composition range 0.32 ≤ x ≤ 0.82

Abstract

The structure of strontium barium niobate crystals SrxBa1-xNb2O6 is comprehensively studied in the whole range of the tetragonal tungsten bronze phase (x=0.32-0.82) using both powder and single-crystal X-ray diffraction measurements. Unit-cell parameters, density, site-occupancy factors and interionic distances show an explicit composition dependence which can be consistently explained using simple model calculations. The temperature dependence of the unit-cell parameters exhibits a remarkable anisotropy in a broad temperature region below the phase transition temperature. This proves that the electrostrictive contribution to the thermal expansion plays an important role in strontium barium niobate.

On the energetics of cation ordering in tungsten-bronze-type oxides

“…Intuitively, the larger ionic radius of Ba 2+ relative to Sr 2+ and Pb 2+ implies that the former will preferentially occupy the larger pentagonal sites, which has also been found experimentally. 6,18 However, even this simple effect of atomic size is not obvious: Large cations preferentially occupy the larger octahedral sites in 4-2 spinels, while the opposite is actually true for 2-3 spinels. 16 There is therefore no guarantee that a simple argument based on atomic size also holds for a different crystal structure such as the TTB-type.…”

Critical slowing down and elastic anomaly of uniaxial ferroelectricCa0.28Ba0.72Nb2O6crystals with tungsten bronze structure

“…The high values of the spontaneous polarization and the electro-optic coefficient of SBN, especially for Sr-rich alloys, are affected by the smaller lattice parameters in comparison to other TTB ferroelectrics [13]. Upon heating from room temperature, SBN undergoes a ferroelectric phase transition from 4mm to 4/mmm [5].…”

“…These may be discussed on the basis of the site occupancy. In a previous study, it has been shown that CBN28 and SBN61 have a similar unit-cell size [13,28]. On the other hand, the Ca 2+ ion radius is 1/ s [21].…”

“…Other consequences of the weaker diffusive nature are the decrease in the index of the extended Curie-Weiss law to 1.65 and the lack of a frequency-dependent high-T shift in the susceptibility peak T m [21]. It was assumed that the outstanding characteristics of SBN are associated with the relatively small lattice parameters [13], whereas CBN actually has lattice parameters smaller than those of SBN. Generally, in REFs, polar nanoregions (PNRs) are formed below the Burns temperature T B upon cooling.…”

Dielectric Relaxation Phenomena in SBN Single Crystals Doped with Ce

“…On the basis of the available structural [21] and dielectric data for related materials [22] one can suppose that the determined values of the relaxation time and the activation energy E a would be related to the collective oscillations of the short strong and long weak Nb-O bonds in the two different type corner-sharing NbO 6 octahedra aligned along c-axis.…”