Key Engineering Materials Vols. 336-338

Abstract: In this present work, we adopt conventional solid state reaction techniques to obtain CaCu3Ti4O12 (CCTO) ceramics and the dielectric properties of polycrystalline CCTO samples sintered in the temperature range 900 − 1100°C were investigated. X-ray diffraction (XRD) patterns show no obvious change in crystal phase with various sintering temperature. However, experimental results show that the dielectric properties of CCTO ceramics are very sensitive to processing parameters and the dependence of dielectric constant and loss tangent of CCTO ceramic on processing can be obtained. The effect of sintering conditions on the surface microstructures and the electrical properties of CCTO ceramics are also discussed in this study.

Abstract: Lithium niobate thin films have been deposited on Pt/Ti/SiO2/Si substrates by the Pechini method from metal carboxylate gels and heat-treated at temperatures ranging from 400 to 600°C. The thermal decomposition of the metal carboxylate precursor gels has been studied by differential thermal analysis and thermogravimetry. The products derived from calcination of the gels at different temperatures have been characterized by Fourier transform infrared, Roman spectrum and X-ray diffraction. Scanning electron microscopy analysis shows the surface of the films to be smooth, dense and crack-free. Electric properties measurement indicates that the LiNbO3 films demonstrate a ferroelectric hysteresis loop. The remanent polarization (Pr) and coercive field (Ec) are 17.89 μC/cm2 and 35.23 kV/cm, respectively.

Abstract: Langasite (La3Ga5SiO14, LGS) and its isomorphs, were regarded as potential substrate materials for surface acoustic wave (SAW) and bulk acoustic wave (BAW) applications. Among these homologous compounds, the ordered structure crystals have attracted much attention for their low Ga2O3 content, high acoustic velocity and low acoustic loss. In this work, the ordered langasite structure crystals Ca3NbGa3Si2O14 (CNGS) were grown with vertical Bridgman method for the first time. The CNGS crystals with 25mm in diameter and 40mm in length were grown successfully from its stoichiometric melt through LGS crystal of Ø10mm×40mm being chosen as seed. X-ray powder diffraction experiments showed that the CNGS single crystals had a single phase and had the same structure as the LGS crystal. The transmittance spectra with the wavelength from 200 to 800nm were recorded by means of Spectrophotometer at room temperature.

Abstract: LSMO films with various thicknesses were prepared on single crystal Si (111) substrates by sol-gel process. The films were dense and had a uniform microstructure. The films showed metallic conduction characteristics at low temperature and insulator characteristics at high temperature. The metal-insulator transition temperatures (Tmi) of the films were remarkably lower than that of the bulk ceramics. The effect is related to the distortion of crystal lattice resulted from the residual stress in the films.

Abstract: Highly dense Na1-xKxNbO3 (x=0.2~0.8) ceramics were successfully prepared using spark plasma sintering (SPS) at temperature as low as 920°C. Solid solutions were formed during the composition range investigated. The piezoelectric constant and planar mode electromechanical coupling coefficient are significantly dependent on the Na/K ratio, with the maximum value of 148 pC/N and 38.9% at the composition Na0.5K0.5NbO3.

Abstract: XRD, SEM, bulk density and dielectric properties measurements were used to investigate the effect of TiO2 nanopowder substitution for conventional TiO2 micro-powder on the sintering and electric properties of PZT ceramics. Results revealed that the sintering temperature of dense Pb(Zr0.53Ti0.47)O3 ceramics was lowered about 50°C ~ 100°C when 20% and 40% of conventional TiO2 micro-powder was substituted by TiO2 nanopowder. The electric properties were kept or even enhanced in the PZT ceramics adopted the TiO2 nanopowder.

Abstract: (1-x)BiScO3-xPbTiO3 (BSPT) based ferroelectric ceramics were prepared by conventional solid state process. X-ray diffraction analysis revealed that the morphotropic phase boundary (MPB) separating the rhombohedral and tetragonal phases for the BSPT system exited near x=0.62. It was found that the stability of perovskite structure of the BSPT system was improved with the increase of PbTiO3 content. For the 0.36BiScO3-0.64Pb1-ySryTiO3 (BSPST) system, because of higher amount of ionic bonding, the stability of perovskite structure for BSPT compounds containing strontium is larger than that of non-strontium compound.

Abstract: Ultrafine (1-x)BiScO3-xPbTiO3 ferroelectric ceramics were successfully prepared by employing nanocrystalline ceramic powder. The average ceramic grain sizes range from 0.4μm to 1.2μm with different phases and different proceeds. The studies show the average grain sizes vary with the calcining and sintering temperature as well as the compositions in different phases. Ceramics, sintered at 1020°C for 3h, in morphotropic phase boundary (MPB) have the smallest grain sizes around 0.4 μm, those in tetragonal phase and rhombohedral phase have larger grains around 0.9μm. Meanwhile, the piezoelectric property and Curie temperature were founded size-dependent when the grain sizes are smaller than 1μm.

Abstract: The precursor powder of lead-zirconate-titanate (PZT) and NiFe2O4 (NFO) was prepared using one step sol-gel method. The dry powders got after a series of processes were sintered via a conventional ceramic solid-state reaction technique. All the diffraction peaks in the XRD patterns of the composites can be readily indexed to NFO and PZT, respectively. The SEM micrograph shows two different phases of PZT and NFO distinctly and the particle size of NFO was about 2~4 μm. The magnetoelectric (ME) coefficient, dielectric constant, piezoelectric constant, magnetic hysteresis loops of the samples were measured. The dc magnetic Hdc resulting in the maximum ME coefficient varies from 0.65kOe to 1.0kOe with the increase of the NFO volume fraction. The maximum magnetoelectric coefficient of 6.15Vcm-1Oe-1 was obtained at resonance frequency of 289.8kHz, dc magnetic intensity of 0.8kOe and NFO volume fraction of 0.25.

Abstract: ZnO films with piezoelectric properties were deposited on polycrystalline diamond wafers for high frequency surface acoustic wave filter applications by dc reactive magnetron sputtering. The influences of different sputtering pressures and substrate temperatures on the properties of ZnO films were discussed. Highly c-axis oriented, fine-grain ZnO films with excellent surface flatness (average surface roughness of 5.3 nm) and high resistivities (6.3×107 *·cm) have been obtained. Then Al films for interdigital-transducer were deposited on ZnO/diamond by electron evaporation, a 2.48 GHz longitudinally- coupled double-mode surface acoustic wave filter has been fabricated using the Al/ZnO film on diamond wafer.