Thermal expansion of SrZrO3 and BaZrO3 perovskites

Abstract

Abstract. High-temperature X-ray diffraction studies of SrZrO 3 and BaZrO 3 perovskites have been carried out to 1200 ~ C. The diffraction patterns are analyzed with Rietveld method so as to refine the unit cell dimensions. The volumetric thermal expansion coefficient are observed to be 2.98.10-SK -1 for orthorhombic Pbnm phase, 3.24.10-5K -1 for orthorhombic Cmcm phase, 3.75.10-SK -~ for tetragonal I4/mcm phase of SrZrO3 perovskite, and 2.06* 10-SK -1 for cubic Pm3m phase of BaZrO3 perovskite, respectively. The linear thermal expansion coefficients of SrZrO 3 perovskite show considerable anisotropy of e, > ec> eb for orthorhombic Pbnm phase, which reflect the decrease of distortion of the perovskite. It is demonstrated that thermal expansion of the centrosymmetrically distorted ABX 3 perovskite can be empirically expressed as a combination of the changes of [B-X] bond length and tilting angle of BX6 octahedral framework. The octahedral tilting is considered to be the primary order parameter for the ferroelastic type of structural phase transitions in perovskite. Thermodynamically, the tilting induced volume change denotes the "excess volume" and the corresponding thermal expansion represents the "excess thermal expansion" for the lower symmetry phase with respect to its prototype of the cubic perovskite.

Intense blue and green photoluminescence emissions at room temperature in barium zirconate powders

“…These results are consistent with the XRD data of crystalline BaZrO 3 powders, N Zr-O = 6, R = 2.09Å [35]. On the other hand, in the case of BaZrO 3 powders heat treated at 773 K, which were characterized as being structurally ordered-disordered based on XRD data, the best fitting of the filtered EXAFS spectra was achieved with a structural model composed by 3 shells with a bond length in the range from 2.06 to 2.31Å (see Table 1 and Fig.…”

“…EXAFS spectrum of crystalline powders is quite similar to that reported in the literature [35]. As can be seen in Fig.…”

“…3(b) was selected and again the Fourier transform was employed to obtain a filtered EXAFS spectrum related only to the first Zr-O coordination shell. The filtered EXAFS spectrum was then fitted using the theoretical phase and amplitude functions provided by the FEFF8.2 code [35]. According to the fitting results presented in Table 1, the first coordination shell around Zr atoms in BaZrO 3 powders heat treated at 973 K is composed by 6 oxygen atoms situated at approximately 2.11Å (see Fig.…”

Structural Phase Transitions between 700 and 850.DEG.C. in SrZrO3 Studied by Raman Spectroscopy

“…The heat capacity and the thermal expansion of SrZrO 3 were determined by Zhao and Weidner 8) and Ligny and Richet.…”

Structure and high-temperature properties of the (Sr,Ca,Y)(Co, Mn)O3−y perovskites — perspective cathode materials for IT-SOFC

“…The difference is smaller for x=0.75: 44 S/cm and 37.6 for M=Mn and M=Fe, respectively [18]. The temperature dependence of the conductivity is different for the Another example is the increase of TEC for SrZrO 3 when it transforms from the low temperature orthorhombic GdFeO 3 modification (TEC v =29.8 ppm K -1 ) to the high-temperature tetragonal one (I4/mcm) (TEC v =37.5 ppm K -1 ) [38]. However, a recent study of the high-temperature crystal structure of SrZrO 3 revealed that its high-temperature cubic modification in fact exhibits a lower TEC v (29 ppm K -1 ) than the orthorhombic modification (TEC v =31.0 ppm K -1 ) [40].…”