Signatures for Coexistence of Monoclinic and Hexagonal Phases in GaTe Nanoflakes

The burgeoning two-dimensional(2D)layered materials provide a powerful strategy to realize efficient light-emitting devices.Among them,gallium telluride(Ga Te)nanoflakes,showing strong photoluminescence(PL)emission from multilayer to bulk crystal,relax the stringent fabrication requirements of nanodevices.However,detailed knowledge on the optical properties of Ga Te varies as layer thickness is still missing.Here we perform thickness-dependent PL and Raman spectra,as well as temperature-dependent PL spectra of Ga Te nanoflakes.Spectral analysis reveals a spectroscopic signature for the coexistence of both the monoclinic and hexagonal phases in Ga Te nanoflakes.To understand the experimental results,we propose a crystal structure where the hexagonal phase is on the top and bottom of nanoflakes while the monoclinic phase is in the middle of the nanoflakes.On the basis of temperature-dependent PL spectra,the optical gap of the hexagonal phase is determined to be 1.849 eV,which can only survive under temperature higher than 200 K with the increasing phonon population.Furthermore,the strength of exciton-phonon interaction of the hexagonal phase is estimated to be 1.24 me V/K.Our results prove the coexistence of dual crystalline phases in multilayer Ga Te nanoflakes,which may provoke further exploration of phase transformation in Ga Te materials,as well as new applications in 2D light-emitting diodes and heterostructure-based optoelectronics.

Monoclinic KNbO3 Nanowires for Photocatalytic Methane Production and Dye Degradation

The room temperature stabled monoclinic KNbO3 nanowires were found to act as photocatalyst for photocatalytic methane production and dye degradation in this work. Higher activities have been observed for monoclinic phase compared to the reference（orthorhombic phase）. In the photoreduction of CO2 reaction, the monoclinic KNbO3 nanowires exhibited a CH4 evolution rate of 0.025 μmol·g-1·h-1, which was higher than 0.021 μmol·g-1·h-1 of orthorhombic KNbO3 nanowires. In the photodegradation of rhodamine B（Rh B）, almost all the Rh B were degraded after 90 min light illumination for monoclinic KNbO3 nanowires. But for orthorhombic KNbO3 nanowires, the concentration of Rh B only decreased to 62% of the initial value.

Synthesis of Monoclinic Form of Gd_(2-x)Na_xCuO_4 by Direct Precipitation from Molten Salt

A new phase of Gd_(2-x)Na_xCuO_4 was synthesized by direct precipitation from the mixture of Gd_2O_3 and CuO in the molten KOH/NaOH/KNO_3 solution at temperature as low as 280℃. The resulting precipitate was characterized by using SEM, XRD, EDX, XPS and magnetic method. The XRD data indicate that the precipitated Gd_(2-x)Na_xCuO_4 is monoclinic with lattice parameters a=8.6816, b=3.7233. c=6.0796. a=γ=90', 0=108.75° and V=186. 13.

The Structure and Properties of Multi-cations Doped KNN-based Piezoelectric Ceramics

The piezoelectric strain of K_(0.5)Na_(0.5)NbO_(3)-based lead-free ceramic at different temperatures was studied.The Rayleigh analysis shows that the intrinsic and extrinsic contributions are increased at temperature from 173 to 298 K.In addition,a monoclinic phase structure was observed at 83 K.The results of phase field simulation show that the temperature dependent microstructure evolution is a function of the local structure size.This work contributes to understanding the structure and properties relationship of the multi-cations doped KNN-based piezoelectric ceramics as a function of temperature.

The nanostructure of barium dititanate prepared by hydrothermal method

The dielectric ceramic of barium dititanate compound BaTi_(2)O_(5) had been prepared through the hydrothermal process by applying different parameters,such as pH-value,reaction time,temperature and pressure.The prepared powders were examined by X-ray diffraction(XRD).The predominant phase was a monoclinic phase with lattice constants(a=16:6381,b=3:555,c=9:3406Å),(β=107:47°,α=γ=90°),and the unit cell volume(527Å^(3)).The surface morphology was demonstrated by Scanning Electron Microscopy(SEM).It exhibited the grains in spherical and elliptical shapes with high homogeneity.The shapes of nanostructure were analyzed by Transmission Electron Microscopy(TEM).The appearance of nanostructures like the nanoparticles and nano rods were found.The size of nanoparticles was in the range of 9–31 nm,and size of nanorods was 32–37 nm.The dielectric measurements were done by using LCR meter at different temperature and frequencies(10,50 and 100 kHz).It was clear that the Curie temperature had a high value up to(485℃).The relative permittivity was partially changed for two prepared samples regarding high pressure and long reaction time,which were the main preparation conditions of hydrothermal method.