Crystal Structure Of Specimens Research Articles

Change in structure and luminescent properties of ZnSe and ZnCdSe films irradiated by electron beam

Layers of ZnSe and ZnCdxSe (x ~ 0.32-0.35) grown on GaAs (001) substrates by molecular beam epitaxy method were investigated. The electron beam impact on changes in crystal structure of specimens under examination and on their luminescent properties was studied. Methods of cathode luminescence, transmission electron microscopy, and electron microprobe analysis were applied. It is found that irradiation of specimens in the transmission electron microscope results in stacking faults annealing accompanied by formation of ZnO precipitates with hexagonal crystal structure. Irradiation of specimens in the cathode luminescence plant results in decreased intensity of cathode luminescence layers of ZnSe and ZnCdxSe in question due to radiation-stimulated degradation processes. Key words: point defects, irradiation by electron beam, cathode luminescence, structural changes.

Effects of Surface Treatment on the Microstructural and Crystallographic Changes of Dental 3Y-TZP Ceramic

Objective: To investigate the effects of different surface treatments on the microstructural and crystallographic changes of dental 3Y-TZP ceramics. Methods: 21 pieces of zirconia specimens (15 ´ 15 ´ 1.5 mm) were prepared and divided into 7 groups: control group; grinding group; polishing group; sandblasting group; sandblasting + veneer porcelain sintering group; sandblasting + veneer porcelain sintering twice group and sandblasting + annealing group. The crystal structure of specimen was monitored by X-ray diffraction (XRD) before morphological observation with scanning electron microscope. Results: monoclinic phase increased after grinding while decreased little after polishing, bigger phase change presented after sandblasting compared with decreased phase change induced by veneer porcelain sintering; annealing eradicated the surface m phase. Grinding produced coarse scratches on the surface of samples with removal of surface particles; after grinding and polishing to 7 um level, the surface particles were removed massively, and the surface became smooth with remaining scare scratches and substantial micro cracks. Sandblasting removed scratches near completely producing coarse and irregular surface of samples. Conclusions: Grinding, sandblasting and polishing could produce the transition of Zirconia Ceramic surface from t to m phase. It is better to use heat treatment after mechanical treatment to reverse the changed surface phase.

Dielectric and Piezoelectric Properties of [Li0.04(Na0.54K0.46)0.96] (Nb0.84Ta0.10Sb0.06)O3 Lead-Free Ceramics as a Function of (Bi,Na)TiO3 Substitution

In order to develop lead-free composition ceramics for piezoelectric actuator, sensor, and transformer applications, (1-x)[Li0.04(Na0.54K0.46)]0.96(Nb0.84Ta0.10Sb0.06)O3 + x(Bi0.5Na0.5)TiO3 (x = 0∼2 mol%) composition ceramics were fabricated by a conventional sintering technique. The influences of (Bi0.5Na0.5)TiO3(abbreviated as BNT) on the microstructure, the dielectric, ferroelectric and piezoelectric properties of the ceramics were investigated. The crystal structure of specimens with x = 0 mol% exhibited an orthorhombic structure. However, at the compositions more than 0.5 mol%, the crystal structure showed tetragonal structure. The temperature dependence of dielectric constant showed that Curie temperature decreased with the increase of BNT substitution content. At room temperature, the ceramics substituted with 1 mol% BNT had a piezoelectric constant d33 = 222.6 pC/N, electromechanical coupling factor kp = 0.36, mechanical quality factor Qm = 78 and dielectric constant ϵr = 1570, respectively.

Application of Chemical State Mapping Technique with Electron Probe X-Ray Microanalyzer for BiSrCaCuO Superconductor

High resolution O–Kα X-ray spectra obtained by electron probe X-ray microanalysis (EPMA) have been found to provide a detailed insight into the crystal structure of specimens. A practical approach for digital color mapping of the crystal structures is proposed, which uses the ratio of the intensities of two specific wavelengths to represent the spectral shape. An application of this approach to digital mapping for a BiSrCaCuO superconductor is presented. The results lead to a more comprehensive understanding of the micro-crystallinity of fine specimens.

Pyroelectric Properties of Lead Antimony Stannate-Lead Titanate-Lead Zirconate Ceramics Modified with La and Mn

In the present study, 0.10Pb(Sb1/2Sn1/2)O3-0.25PbTiO3-0.65PbZrO3 ceramics modified with La2O3 (1 mol%) and MnO2 (0∼0.30 mol%) were fabricated, and the structural and pyroelectric properties with different amounts of MnO2 were studied. The crystal structure of specimens was rhombohedral, and average grain sizes decreased with increasing amounts of MnO2. The (Pb0.99La0.01)[(Sb1/2Sn1/2)0.10Ti0.25Zr0.65]O3 specimen modified with 0.24 mol% MnO2 showed a large pyroelectric coefficient, p, (=6.73×10-8 C/cm2 K) and voltage responsivity, Rv, (=125 V/W). Also, in the same specimens, noise equivalent power, NEP, and detectivity, D*, were 2.376×10-7 W/Hz1/2 and 6.793×106 cm Hz1/2 W, respectively. In the (Pb0.99La0.01)[(Sb1/2Sn1/2)0.10Ti0.25Zr0.65]O3 specimens modified with 0.24 mol% MnO2 voltage responsivity decreased with increasing chopper frequency, and was independent of the thickness of the specimens.