Crystallographic studies of perovskite-like compounds. II. Rare earth alluminates

Abstract

The aluminates of the trivalent ions of Gd, Eu, and Sm are isostructural with GdFeO 3. They belong to space group YD~-Pbnm with four distorted perovskite units in the true crystallographic cell. The aluminates of the trivalent ions of Nd, Pr and La are rhombohedral belonging to space group D~d--R3m with two formula units in the unit cell. These crystals bear a very close structural relationship to the orthorhombie ones.LaA103 undergoes a transition at 435±25 ° C. to the simple cubic cell containing one formula unit. Evidently, the transition is one of higher than first order. There is no crystallographic transition of PrAI03 below 950 ° C. but a gradual change toward the cubic phase similar to that in LaAl03 is indicated. 1020 CRYSTALLOGRAPHIC STUDIES OF PEROVSKITE-LIKE COMPOUNDS. II

First-principles study of polar LaAlO (001) surface stabilization by point defects

“…The electronic total energy is converged within 10 -6 eV/cell for each electronic self-consistent field calculation. Experimentally, the ground state structure of LAO below 820K is a rhombohedral perovskite ( c R3 ) with the tilted AlO 6 octahedra network [41][42][43][44]. We calculate the rhombohedral cell angle α in the ground state structure to be 60.1°.…”

Synthesis and characterization of lanthanum monoaluminate by co-precipitation method

“…Its use as a gate dielectric material has also been explored [10,11] .In addition, LaAlO 3 powder has been studied as a catalyst for oxidative coupling of methane and hydrogenation and hydrogenolysis of hydrocarbons due to its high catalytic activity [12].Polycrystalline LaAlO 3 has been commonly prepared by a solidstate reaction method: i.e. direct mixing and firing of pure oxides of La 2 O 3 and Al 2 O 3 at temperature greater than 1550 •C [13][14][15][16]. The full development of the LaAlO3 phase has been exercised by only heating the sample to 1600 •C and then reheating to 1750 •C for 3 h to form a polycrystalline disk.…”

“…Chemical coprecipitation route is a simple method for synthesizing nanopowders [25].The base precipitant most used in this method is NH 4 OH. Recently, Li et al [17]; Nair et al [26]; and Kuo et al [8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27] have used this method to synthesize pure LaAlO 3 using the mixed solution of NH 4 OH and calcined at 700, 800 and 1000 •C, respectively. However, the synthesis of lanthanum monoaluminate has been rarely reported using a mixture of sodium hydroxide such as base precipitant In the present study, nanocrystalline LaAlO 3 powders have been successfully synthesized using the mixed solution of NaOH in low temperature range of 500-1000 •C and pH 9.…”

“…LaAlO 3 with a perovskite-type structure [9] is widely used as substrates and electrically insulating buffers for depositing high-temperature superconducting films due to its high quality factor and excellent lattice and thermal expansion matching ability [2,6]. Its use as a gate dielectric material has also been explored [10,11] .In addition, LaAlO 3 powder has been studied as a catalyst for oxidative coupling of methane and hydrogenation and hydrogenolysis of hydrocarbons due to its high catalytic activity [12].Polycrystalline LaAlO 3 has been commonly prepared by a solidstate reaction method: i.e.…”

The ASnO3 (A=Ca,Sr) perovskites

“…Among them are rhombohedral, as the LaAIO3 phases (Geller & Bala, 1956), orthorhombic, like the rare-earth orthoferdtes (Marezio, Remeika & Dernier, 1970) and the mineral perovskite CaTiO 3 (Kay & Bailey, 1956) which gives the name to the whole family.…”