Minori Taguchi

Synthesis of monocarboxylic acid-modified CeO2 nanoparticles using supercritical water

This study reports a simple, rapid synthesis technique for the preparation of monocarboxylic acid-modified CeO2 nanoparticles. The nanoparticle products were prepared under hydrothermal conditions using supercritical water and Ce(OH)4 as a precursor in the presence of monocarboxylic acids with different alkyl chain lengths (C6–18) acting as surface modifiers. The precursor and surface modifiers were heat-treated in a batch-type reactor at 400 °C for 30 min. The carboxylic acids attached to the surface of the products by coordination bonds between the carboxylate (–COO−) and Ce ions. The amount of attached surface modifiers tended to increase with increasing alkyl chain length. The products exhibited a cubic morphology and particle sizes of approximately 10 nm, controlled by the surface modifiers. Surface modification also controlled the band gap of the products, suggesting the possibility of tuning their electronic and optical properties by using organic surface modifiers.

Multistage ordering and critical singularities inCo1−xZnxAl2O4(0≤x≤1): Dilution and pressure effects in a magnetically frustrated system

We report comprehensive studies of the crystallographic,magnetic, and thermal properties of a spinel-type magnetically frustrated compound, CoAl2O4, and a magnetically diluted system,Co1-xZnxAl2O4. These studies revealed the effects of dilution and disorder when the tetrahedral magnetic Co ion was replaced by the nonmagnetic Zn ion. Low-temperature anomalies were observed in magnetic susceptibility at x<0.6. A multicritical point was apparent at T = 3.4 K and x = 0.12, where the antiferromagnetic, spin glass-like, and paramagnetic phases met. At that point, the quenched ferromagnetic component induced by a magnetic field during cooling was sharply enhanced and was observable below x = 0.6. Around x = 0.6, magnetic susceptibility and specific heat were described by temperature power laws, chi ~ C/T ~ T-d, in accord with the site percolation threshold of the diamond lattice. This behavior is reminiscent of a quantum critical singularity. We propose an x-temperature phase diagram in the range 0<x<1 for Co1-xZnxAl2O4. The transition temperature of CoAl2O4 determined from magnetic susceptibility measured under hydrostatic pressure increased with increasing pressure.