Jeong-Ryeol Kim

Phase Constitutions and Microwave Dielectric Properties of Zn3Nb2O8-TiO2.

The phase constitutions and microwave dielectric properties of (1-x)Zn3Nb2O8–xTiO2 were investigated using X-ray powder diffraction and a network analyzer, respectively. Four mixture regions were studied with increasing TiO2 content (x): (1) Zn3Nb2O8, ZnNb2O6, and Zn2TiO4, (0<x≤0.5) (2) ZnNb2O6 and Zn2TiO4, (0.5<x<0.65) (3) Zn2TiO4, ZnTiNb2O8, and TiO2 (0.65≤x≤0.75), (4) Zn2TiO4 and TiO2 (0.75<x<1). This structural evolution with composition was ascribed to the interrelations between Zn3Nb2O8 and TiO2. It was demonstrated that the microwave dielectric properties correlated to crystal structure rather than chemical composition. In the mixture region of Zn2TiO4, ZnTiNb2O8, and Zn2TiO4, the amount of TiO2 and ZnTiNb2O8 considerably increased and decreased, respectively, with increasing TiO2 content (x). This resulted in the increase of relative dielectric constant (er) and temperature coefficient of resonant frequency (τf). At x=0.725, Q×f is 5190 GHz, er and τf are 36 and 4 ppm/°C, respectively.

Enhancing photocatalytic activity by using TiO2–MgO core-shell-structured nanoparticles

Hygroscopic Mg(OH)2 gel was topotactically decomposed on TiO2 particle surfaces, resulting in highly nanoporous MgO-coated TiO2 particles. The highly hygroscopic and nanoporous MgO shell absorbed more water molecules and hydroxyl groups from the environment to yield an improved photocatalytic property of the core-shell particles as compared to the uncoated TiO2 counterpart.