Dielectric Properties of Alkoxy-Derived BaTiO3 Films on LaNiO3/Pt/TiOx/Si(100)
BaTiO3 films with higher degrees of (100) orientation were deposited using both of the heterogeneous LaNiO3 nucleation layer and homogeneous BaTiO3 buffer layer. The microstructure and dielectric properties are characterized. The temperature dependence of the dielectric properties is additionally discussed. The alkoxy-derived 1-mum thick BaTiO3 had the unique microstructure and showed predominant (100) orientation. The film showed ferroelectric to paraelectric transition around at 105degC, and improved dielectric properties. The improvement is considered to be due to the simultaneous control of crystallographic and microstructural characteristics by using the double nucleation and buffer layers.
Dielectric Properties of BaTiO3 Thin Films Derived from Clear Emulsion of Well-Dispersed Nanosized BaTiO3 Particles
The dielectric properties of thin films with microemulsion (ME)-routed nanocrystalline BaTiO3 particles were investigated in terms of the films' crystallinity and grain size. The ME method provided a clear emulsion of well-dispersed nanocrystalline BaTiO3 particles. BaTiO3 thin films were prepared by direct spin-coating of the clear emulsion on Si/SiO2/Al2O3/Pt substrates. By varying the postannealing temperature from 600°C to 1000°C, BaTiO3 thin films of different grain sizes were prepared. A fine BaTiO3 powder was removed from the clear emulsion by adding ammonia solution to cause flocculation, followed by centrifugation and washing. A transmission electron microscope (TEM) observation revealed that the powder generated many inner voids, but the thin films did not contain inner voids, thus resulting in high crystallinity. The dielectric properties of these films were measured as functions of temperature. Polarization as a function of voltage was measured, and a ferroelectric D-E hysteresis curve was observed in the sample with a mean grain size of 18 nm. The measurement of piezoelectric hysteresis using a scanning probe microscope (SPM) also revealed ferroelectricity in a small area just below the SPM probe. Direct use of the clear emulsion of well-dispersed nanocrystalline BaTiO3 particles in the ME method enables the fabrication of BaTiO3 thin films that consist of nanocrystalline BaTiO3 grains without inner voids, and the films exhibit great dielectric performance.
ROOM- AND HIGH-TEMPERATURE MAGNETIC PROPERTIES OF Sm(CobalFexCu0.088Zr0.025)7.5 (x=0.30) SINTERED MAGNETS
The effect of Fe content on room- and high-temperature magnetic properties of Sm(CobalFexCu0.088Zr0.025)7.5 (x=0-0.30) sintered magnets, prepared by the conventional powder metallurgy method, has been systematically studied. With increasing Fe content, the remanences BT and maximum energy products (BH)max at room temperature gradually increase and reach optimal values of 1.055 T with x=0.27 for BT, and 205 kJ/m3 with x=0.21 for (BH)max, respectively, and then drop sharply with further Fe increase. An excessive addition of Fe (x≥0.24) results in rapid deterioration of permanent magnetic properties due to the formation of a considerable amount of FeCo soft magnetic phase. It was found that the effect of Fe content on high temperature stability is huge. The lower the Fe content, the smaller the temperature coefficient of coercivity. When x=0.07, a temperature coefficient of coercivity of -0.14%/K (293-723 K) can be achieved, as compared with -0.23%/K for x=0.21. BT of 0.725 T, bHc of 517 kA/m, iHc of 764 kA/m, and (BH)max of 95 kJ/m3 at 723 K were obtained, and the B-H demagnetization curve remains a straight line.