Effects of raw materials on NaNbO₃ nanocube synthesis via the solvothermal method

Abstract

A nanocube is a single nanoscale crystal with a cubic shape. Raw materials are an important factor in determining the synthesis of nanocubes. In this study, we investigated various niobium compounds that serve as raw materials, each inducing different effects during nanocube synthesis. Perovskite sodium niobate (NaNbO 3 ) nanocubes were synthesized using a two-step process. The first step in this process, synthesis of the raw materials, was followed by solvothermal synthesis of NaNbO 3 nanocubes. The raw material for the first step was obtained by applying heat treatment to a precursor following Nb hydrolysis. The heat treatment was performed at temperatures of 300-1000°C. Nb 2 O 5 was obtained after heat treatment of its precursor, during which its crystalline system morphed into hexagonal, orthorhombic, and monoclinic systems with respective increases in temperature. For the second step, we obtained various NaNbO 3 morphologies via the solvothermal method using water, methanol, or ethanol as a reaction medium. NaNbO 3 nanocubes were formed by applying the solvothermal method to the synthesized precursor during heat treatment at 800°C. Solvothermal synthesis was performed with methanol as the reaction medium at 200°C, which resulted in the formation of NaNbO 3 nanocubes. ARTICLE HISTORY

Solvothermal synthesis and morphology control of NaNbO3 nanocubes using a reaction medium of water and/or methanol

“…As regards the NaNbO 3 , the synthesis of cubic [10] or nanowire [11] NaNbO 3 was studied using a hydrothermal reaction or calcination, respectively. The effect of the starting material on NaNbO 3 nanocube synthesis via the solvothermal method has also been reported recently [12]; in that case, however, the NaNbO 3 nanocubes were synthesized using a two-step solvothermal process and only one reaction medium (i.e. methanol).…”

“…The starting material was obtained by hydrolysis of metallic Nb to form a precursor solution, followed by heat treatment of the obtained precursor solution [12][13][14]. Metallic Nb (5 mmol) was dissolved in 60 ml of hydrogen peroxide (H 2 O 2 , purity: 30.0-35.5%; Kanto Chemical Co., Inc., Tokyo, Japan) and 15 ml of ammonia solution (NH 3 , purity: 28.0-30.0%; Kanto Chemical Co., Inc.) in an ice bath.…”

“…As regards the starting material, particles with low solubility that initially adopt a perovskite structure tend to become nanocubes during solvothermal synthesis [8,12]. We examined morphology control of NaNbO 3 via the solvothermal method based on this knowledge.…”

Understanding the Hydrothermal Formation of NaNbO3: Its Full Reaction Scheme and Kinetics

“… 11 Ex situ studies of the hydrothermal synthesis of NaNbO 3 12 − 17 have shown that the reaction starts with the transformation of the T-Nb 2 O 5 (orthorhombic structure) precursor into sodium hexaniobate (HNa 7 Nb 6 O 19 ·15H 2 O), with the main building block consisting of the Lindqvist ion, [Nb 6 O 19 ] 8– . 18 The sodium hexaniobate then transforms into Na 2 Nb 2 O 6 ·H 2 O, which in turn transforms into perovskite NaNbO 3 , displaying a wide range of morphologies including cubes 19 − 21 and various agglomerated structures. 17 , 22 , 23 The crystal structures of these phases are significantly different from each other, as seen in Figure S1 in the Supporting Information, and it is not clear how the structures evolve from one phase to the next or how they affect the growth mechanism of NaNbO 3 .…”

Hydrothermal Synthesis of Iridium-Substituted NaTaO3 Perovskites

“…Some control of crystallite morphology has proved possible; for example, it has been shown that a low concentration of Nb 2 O 5 as a precursor leads to nanorods or nanoplates of NaNbO 3 , while a lower concentration of NaOH yields cubes [20]. Crystallite morphology of NaNbO 3 can also be influenced by the choice of niobium oxide precursor [21], the pH of the solution [22], and the choice of solvent [23]. For electroceramics, fine-grained ceramics can be produced by annealing the powders from hydrothermal reactions: piezoelectric ceramics formed from hydrothermally prepared alkali niobates and tantalates have shown characteristics comparable to ceramics made by conventional methods, but with the advantage of lower sintering temperatures to achieve densification [24][25][26].…”