Solvothermal synthesis of perovskites and pyrochlores: crystallisation of functional oxides under mild conditions

Abstract

In this critical review we consider the large literature that has accumulated in the past 5-10 years concerning solution-mediated crystallisation of complex oxide materials using hydrothermal, or more generally solvothermal, reaction conditions. The aim is to show how the synthesis of dense, mixed-metal oxide materials, usually prepared using the high temperatures associated with solid-chemistry, is perfectly feasible from solution in one step reactions, typically at temperatures as low as 200 °C, and that important families of oxide materials have now been reported to crystallise using such synthetic approaches. We will focus on two common structures seen in oxide chemistry, ABO(3) perovskites and A(2)B(2)O(6)O' pyrochlores, and include a systematic survey of the variety of chemical elements now included in these two prototypical structure types, from transition metals, in families of materials that include titanates, niobates, manganites and ferrites, to main-group elements in stannates, plumbates and bismuthates. The significant advantages of solution-mediated crystallisation are well illustrated by the recent literature: examples are provided of elegant control of crystal form from the nanometre to the micron length scale to give thin films, anisotropic crystal morphologies, or hierarchical structures of materials with properties desirable for many important contemporary applications. In addition, new metastable materials have been reported, not stable once high temperatures and pressures are applied and hence not amenable using conventional synthesis. We critically discuss the possible control offered by solvothermal synthesis from crystal chemistry to crystal form and how the discovery of new materials may be achieved. Computer simulation, combinatorial synthesis approaches and in situ methods to follow crystallisation will be vital in providing the predictability in synthesis that is needed for rational design of new materials (232 references).

Large Scale Nanoparticle Screening for Small Molecule Analysis in Laser Desorption Ionization Mass Spectrometry

“…Nanoparticles gained renewed attention with the success of nanostructure-based surface ionization, such as desorption/ionization on silicon (DIOS) 3 and nanostructure-initiator mass spectrometry (NIMS). 4 Encouraged by this success and the advancement of various nanoparticle synthesis, 5 the use of NPs for LDI-MS, termed nanoparticle-assisted LDI-MS or NALDI-MS, has flourished in recent years. 2,6 Gold and silver NPs have been most widely adopted, thanks to the availability of various synthetic routes, 6−9 but the field has recently expanded into a wider range of NPs, including metal oxide NPs (e.g., TiO 2 ZnS, 19 HgTe 20 ).…”

Synthesis of Rare Earth Niobate and Tantalate Powders via a Peroxo Complex Route

“…Similar behavior of the direct crystallization of LaTaO 4 was observed for the precursor prepared by the PC method, a powerful method to achieve homogeneous distribution of elements (Figure 1). In a solid-state reaction between La(OH) 3 and Ta 2 O 5 , no reactions except for dehydration of La(OH) 3 to form La 2 O 3 proceeded because the heat treatment at 1273 K without keeping time was not sufficient for diffusion of La and Ta to form LaTaO 4 ( Figure S2). These results indicate that La and Ta ions are homogeneously distributed in the precursor prepared by the peroxo method as well as the PC precursor.…”

“…Crystals of ammonium peroxo niobium or tantalum, (NH 4 ) 3 4 ] solution under stirring and white precipitate formed immediately. After 1 h of aging, the precipitate was collected and washed with water three times by a centrifugal method.…”

Analysis of Biomolecules through Surface‐Assisted Laser, Desorption/Ionization Mass Spectrometry Employing Nanomaterials

“…27,28 Briefly, two main ways could be used for their preparation -either the bottom-up approach by disintegration of bulk materials or top-down by synthesis from atomic or molecular species. 29 Metal and metal oxide NPs for SALDI MS are usually synthesized by hydrothermal synthesis which provides the most controllable method for the production of high quality NPs with a defined size.…”