Metastability of the K2NiF4 type structure of the solid solution LaCa(CrxAl1−x)O4(0⩽x⩽0.10)

X-Ray Diffraction Study of the Decomposition Process Occurring in Single Crystals of the K2NiF4-Type Aluminate LaCaAlO4

“…The matrix reflections are well defined and look like those given by a bulk scattering, i.e., the single crystal of LaCaAlO . The a parameter along the rotation axis is found to be close to 3.72 A > , in agreement with the powder data (9). Besides these reflections, the existence of a partial powder diffraction diagram gives evidence of the presence of some LaCaAlO phase which is spread on the surface.…”

“…When a sintered powder was heated for more than 10 h at 1400°C in air, the perovskite-type parent phase LaAlO was unambiguously identified from X-ray powder diffractograms. This specific behavior of LaCaAlO -YCaAlO and LaSrAlO are stable at 1400°C-was discussed in terms of an enhancement of the crystal chemical constraints in the K NiF -type structure, owing to the simultaneous presence of La> and Ca> in the (RS) layer (9).…”

“…In any case, for such so-called P phases, the values of the a -type parameters are close to 3.95 and 4.03 A > , respectively. The value 4.03 A > is likely to take into account the elongation of the (P) octahedral layer in the intergrowth structure of LaCaAlO , which results in apical Al-O distances close to 2.03 A > and consequently, a corresponding value of a equal to 4.06 A > (9).…”

“…Under these conditions, it is of importance to learn more about the thermal stability of these aluminates. Recently, the metastability of LaCaAlO was reported (9). When a sintered powder was heated for more than 10 h at 1400°C in air, the perovskite-type parent phase LaAlO was unambiguously identified from X-ray powder diffractograms.…”

Stability and microwave dielectric characteristics of (Ca1−x Sr x )LaAlO4 ceramics

“…The stability of this structure has attracted much attention, and the existence of K 2 NiF 4 type structure is associated with the crystal chemical constraints originating in the 1:1 intergrowth of the rock-salt layer and perovskite layer. These constraints are mainly assumed to depend on steric and chemical effects related to the simultaneous presence of A 3+ , B 3+ and C 2+ cations in the KF layers [8,16,17]. As reported previously by Smirnov et al [19], CaLaAlO 4 crystal is of metastability and will decompose into LaAlO 3 -like phase at 1,200°C. In this article, the stability of some formerly investigated MRAlO 4 (M=Sr and Ca; R=Nd, Sm, and Y) ceramics with K 2 NiF 4 structure is discussed [20][21][22], and (Ca 1−x Sr x ) LaAlO 4 ceramics are prepared along with the determination of microwave dielectric properties and microstructure, as well as the effects of Sr substitution for Ca on the stability of K 2 NiF 4 structure.…”