A “Green Chemistry” Approach to the Synthesis of Rare‐Earth Aluminates: Perovskite‐Type LaAlO3 Nanoparticles in Molten Nitrates

Abstract

Perovskite‐type LaAlO3 nanoparticles have been prepared by a facile, rapid, and environmentally friendly molten salts method using alkali metal nitrates as low‐temperature fluxes. Starting from hydrated lanthanum and aluminum nitrates and alkali metal hydroxides, the proposed methodology consists briefly of two steps: a mechanically induced metathesis reaction followed by short firing at temperatures above nitrates melting points. The purpose of the first is twofold: on the one hand to generate in situ the alkali metal nitrate flux and on the other hand, to obtain a La and Al‐containing precursor material suitable for the synthesis of bulk LaAlO3 nanoparticles in molten nitrates. Different alkali metal nitrates and eutectic mixtures were used to analyze the influence of melt basicity in the reaction outcome. Single phase LaAlO3 was obtained directly, without any purification step when using three molten media: LiNO3, NaNO3, and their mixture; using KNO3 as flux either alone or as part of eutectic compositions, prevents complete conversion, and the title material is obtained mixed with additional crystalline phases such as lanthanum hydroxinitrates and carbonates. As‐prepared LaAlO3 powders are composed of loosely agglomerated nanoparticles with very fine crystallite size (32–45 nm). The present method reduces considerably previously reported synthesis time/temperatures for this material.