Perovskites phases

L. E. Erancis, Sol-Gel Processing, Perovskite Phase Development and Properties ofKelaxor-Based Thin-EajerFerroelectrics, Ph.D. dissertation. University of Illinois, Urbana, 1991. 

The majority of radionuclides (>90%) generated during in-reactor burning are retained in the U oxide matrix hence, their release should be closely related to the corrosion rate of the matrix. The release of Cs and I are generally independent of the fuel corrosion rate, and the metallic elements (Mo, Ru, Tc, Rh, Pd), Xe-Kr gas bubbles, and perovskite phases ((Ba,Sr)Zr03) may only be partly controlled by the matrix corrosion rate. 

Under some in-reactor conditions, other oxide phases, including perovskite phases (ideally AB03), may form. These are known to contain Ru, Zr, Ba, U, and Pu (Kleykamp 1985 Thomas et al. 1992)... 

Perovskites AB)/3C2/303 (A = Ba, Sr, B = Zn, Mg, Co, Ni C = Nb, Ta) are promising compounds for microwave applications. It is important to synthesize these complex oxides as pure perovskite phases because the slightest admixture of a second phase hinders drastically the dielectric properties of ceramics, which sinter only at very high temperatures (1400 to 1500°Q. The precursor chemistry resembles greatly that of BaTi03 formation by alkoxide or alkoxide-hydroxide routes. Below we summarize the 3 approaches to the synthesis of these perovskites by the sol-gel method ... 

Just as in the above described case of BaTi03 preparation, the reaction can be performed in two steps at first bimetallic alkoxide is hydrolyzed, and then Ba(OH)2 is adsorbed by the precipitate of hydrated oxides. Crystallization ofthe perovskite phase under these conditions occurs at 80 to KXPC [1779, 805],... 

Characterization.— The LSFTO powder was calcined at a series of temperatures (1250, 1300, and 1400°C) in air to investigate phase purity and densification behavior. X-ray diffraction (XRD) powder patterns are shown in Fig. 1. The sample is single phase after heating at 1250°C. At the higher sintering temperatures, the lines become sharper and the density increases. The density measured by the Archimedes method was 90.3% relative to theoretical value after annealing at 1400°C for 10 h. The XRD pattern sintered at 1400°C was completely indexed with a cubic unit cell with lattice parameter a = 3.898(8) A and V= 59.2(6) A3. The weak XRD peaks at 31, 43, 55, and 65° 20 are also from the perovskite phase and arise from a small amount of WL radiation in the incident beam. 

Chandler CD et al Precursor for perovskite-phase mixed-metal oxides 1993 [54]... 

Another class of important materials with oxygen ion conduction are perovskites (see Section 2.4.4). Perovskite phases have been, initially, considered as possible electrode materials for SOFCs. The first report of the existence of oxide conductivity in a perovskite material was made using a calcium-doped lanthanum aluminate [98], But the discovery of attractive oxygen conduction properties is rather recent [84],... 

Temperature and period of calcination in air sufficient for obtaining a single perovskite phase. 

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