Composite-Hydroxide-Mediated Approach for the Synthesis of Nanostructures of Complex Functional-Oxides

Abstract

We demonstrate a generic approach for the synthesis of single-crystal complex oxide nanostructures of various structure types, such as perovskites, spinels, monoclinic, corundum, CaF 2 structured, tetragonal, and even metal hydroxides. The method is based on a reaction between a metallic salt and a metallic oxide in a solution of composite-hydroxide eutectic at ∼200°C and normal atmosphere without using an organic dispersant or capping agent. The synthesis technique is cost-effective, one-step, easy to control, and is performed at low temperature and normal atomospheric pressure. The technique can be expanded to many material systems, and it provides a general, simple, convenient, and innovative strategy for the synthesis of nanostructures of complex oxides with important scientific and technological applications in ferroelectricity, ferromagnetism, colossal magnetoresistance, fuel cell, optics, and more.Complex oxides with structures such as perovskite, spinel, and garnet have many important properties and applications in science and engineering, such as ferroelectricity, ferromagnetism, colossal magnetoresistance, semiconductors, luminance, and optoelectronics. 1-6 Nanostructures (nanoparticles, nanowires, and nanobelts) of complex oxides have attracted much attention because of their size-induced novel properties. Although some synthesis methods are successful for fabricating single-cation oxide nanocrystals, 7-14 only a limited amount of work is available for synthesizing nanostructures of complex oxides (with two or more types of cations) because of difficulties in controlling the composition, stoichiometry, and/or crystal structure. The existing techniques rely on high pressure, salt-solvent-mediated high temperature, surface-capping agent, or organometallic precursormediated growth process, 15-24 and the types of oxides that can be synthesized are rather limited. Therefore, seeking a simple approach for low-cost, lower-temperature, large-scale, controlled growth of oxide nanostructures at atmospheric pressure is highly desired, and it is important for exploring zero-and one-dimensional complex oxide-based nanostructures for applications in nanodevices and nanosystems.Here we report a general and widely applicable approach for the synthesis of complex oxide nanostructures of scientific and technological importance. The method is based on a reaction between a metallic salt and a metallic oxide in a solution of molten mixed potassium hydroxide and sodium hydroxide eutectic at ∼200°C and normal atmosphere without using an organic dispersant or capping agent. This methodology provides a one-step, convenient, low-cost, nontoxic, and mass-production route for the synthesis of nanostructures of functional oxide materials of various structure types.We now use the synthesis of two families of complex oxides, perovskite (ABO 3 ; A x A′ 1-x BO 3 ; AB x B′ 1-x O 3 ) 25 and spinel (AB 2 O 4 ), to illustrate the principle and applications of the approach. The sources of A and A′ cations are from metallic salts, ...

Functional Nanowires

“…Besides the syn thesis of conventional binary oxides (discussed by J. Wang et al in this issue), methods have been developed to synthesize NWs of functional and smart ma terials. Liu et al 41 have demonstrated a generic approach for the synthesis of single -crystal complex oxide nanostructures of perovskites, spinels, and various hydroxides, including monoclinic, corundum, CaF 2 -struc tured, tetragonal, and metal hydroxides. 42,43 The method is based on a reaction between a metallic salt and a metallic oxide in a solution of composite hydroxide eutectic at ϳ200ЊC and 1 atm without using an organic dispersant or capping agent.…”

A surfactant-free route to synthesize Ba x Sr1−x TiO3 nanoparticles at room temperature, their dielectric and microwave absorption properties

“…Several chemical methods have been developed for the low-temperature preparation of micro-and nano-sized perovskite crystals such as molten salt synthesis [9][10], solvothermal and hydrothermal method [11][12][13][14][15][16][17], decomposition of bimetallic alkoxide precursors [18][19][20], microwave route [21][22][23][24], and biosynthesis [25]. Though these routes offer successful synthesis of perovskite nanoparticles with high quality and good crystalline, they usually require temperatures higher than 100°C or expensive reactants.…”

Synthesis of Ba-doped CeO2nanowires and their application as humidity sensors

“…The Ba-doped CeO 2 is synthesized through the newly invented nanomaterial fabrication route of the CHM method [11][12][13][14][15]. In a typical reaction, a 9 g amount of mixed NaOH and KOH with a Na/K ratio of 51.5:48.5 is placed in a 25 ml covered Teflon vessel.…”