Tailoring phase transition temperatures in perovskites via A-site vacancy generation

Abstract

The structures across the SrTiZrNbO, 0 ≤ x ≤ 0.6, defect perovskite series were investigated using complementary synchrotron X-ray and neutron powder diffraction data. The locations of second order compositional and temperature dependent phase transitions between the high symmetry cubic Pm3[combining macron]m phase and the lower symmetry tetragonal I4/mcm phase were determined. Deviation of the oxygen x coordinate from the high symmetry value and the B-O-B bond angle from 180° as well as the tetragonal strain squared were each found to be suitable order parameters to monitor the transitions. Tolerance factor calculations confirmed that these A-site deficient perovskites retain a higher symmetry to a lower value than their fully occupied counterparts. Therefore, adjusting vacancy concentrations can be employed as a general strategy to design compounds with specifically tailored phase transition temperatures.

Ferroelectric-Relaxor Crossover and Energy Storage Properties in Sr2NaNb5O15-Based Tungsten Bronze Ceramics

“…In this sense, even if HT presents a single relaxor peak, it could still be regarded as the dissolution of PNRs in the ferroelectric matrix, and the same applied for GT. The existence of vacancies allows higher symmetry of GV, and similar phenomena embodied in Sr 0.8 Ti 0.6– x Zr x Nb 0.4 O 3 have also been reported . Thus, for filled and unfilled ceramics, although the variation of the dielectric behavior with the composition is close, the consequences are completely different, and may be further reflected in the energy storage performance.…”

“…The existence of vacancies allows higher symmetry of GV, and similar phenomena embodied in Sr 0.8 Ti 0.6−x Zr x Nb 0.4 O 3 have also been reported. 42 Thus, for filled and unfilled ceramics, although the variation of the dielectric behavior with the composition is close, the consequences are completely different, and may be further reflected in the energy storage performance. For example, even though the dielectric data of HT3 and GV3 are very similar, the former is only indexed to the space group Im2a like GT.…”

Synthesis and in situ ion irradiation of A-site deficient zirconate perovskite ceramics

“…Ba 0.9 La 0.1 ZrO 3 ) or the correct ratio (ignoring the presence of vacancies, as suggested by Ganguly et al 79 ) reduces t below the ideal BaZrO 3 value of z1, but is still in the regime for perovskite formation. As Whittle et al 80 report, vacancy defects can occupy more space than a fully-occupied cation lattice site, which is contrary to both these calculations. Without a tolerance factor that truly incorporates a specic vacancy-type defect, such calculations can never be considered accurate.…”

Multi-analyser detector (MAD) for high-resolution and high-energy powder X-ray diffraction

“…The structure models consisted of three phases of STN. The main phase, Sr 3 Nb 4 TiO 15 , crystallizes with space group Pna2 1 (Whittle & Schmid, 2014;Whittle et al, 2017). Additionally, two impurity phases were identified.…”