A. R. Raju

Growth and ferroelectric properties of Bi2VO5.5 thin films with metallic LaNiO3 electrodes

Novel ferroelectric bismuth vanadate, Bi2VO5.5 (BVO), thin films have been grown between lattice matched metallic LaNiO3 (LNO) layers deposited on SrTiO3 (STO) by the pulsed laser deposition technique. LNO/BVO/LNO/STO and Au/BVO/LNO/STO trilayer structures exhibited c‐oriented (001) growth of BVO. LNO has been found to be a good metallic electrode with sheet resistance ∼20 Ω in addition to aiding c‐axis oriented BVO growth. The dielectric constant, er of LNO/BVO/LNO/STO, at 300 K was about 12. However, when an Au electrode was used on top of BVO/LNO/STO film, it showed a significant improvement in the dielectric constant (er=123). The ferroelectric properties of BVO thin films have been confirmed by hysteresis behavior with a remnant polarization, Pr=4.6×10−8 C/cm2 and coercive field, Ec=23 kV/cm at 300 K.

Grain size effects on the dielectric properties of ferroelectric Bi2VO5.5 ceramics

Dielectric properties and microstructural characteristics of ferroelectric bismuth vanadate (Bi2VO5.5) ceramics exhibiting grain sizes of 7, 10, 20 and 25 μm have been studied. Microstructural studies indicate the presence of ferroelectric 90° domain patterns on the surface as well as in the bulk of the coarse-grained ceramics. The dielectric constant and the loss tangent both at room temperature and in the vicinity of the Curie temperature have been found to increase with increasing grain size. The Curie temperature (725 K) is found to shift slightly (by about 7 K) towards higher temperatures as the grain size increases (7–25 μm). The magnitude of the dielectric anomaly around 725 K is found to be higher for coarse-grained ceramics. The dielectric constant and the loss have been found to decrease with increase in frequency (1–100 kHz) for all the ceramics studied. The increase in dielectric constant with increasing grain size is attributed to a decrease in thickness of the relatively more insulating grain boundary layer.

Sub-micrometre spherical particles of TiO2, ZrO2, and PZT by nebulized spray pyrolysis of metal-organic precursors

Nebulized spray pyrolysis of metal-organic precursors in methanol solution has been employed to prepare powders of TiO2, ZrO2 and PbZr0.5Ti0.5O3 (PZT). This process ensures complete decomposition of the precursors at relatively low temperatures. The particles have been examined by scanning and transmission electron microscopy as well as X-ray diffraction. As prepared, the particles are hollow agglomerates of diameter 0.1-1.6 mu m, but after heating to higher temperatures the ultimate size of the particles comprising the agglomerates are considerably smaller (0.1 mu m or less in diameter) and crystalline.

Oriented ferroelectric thin films of PbTiO3, (Pb,La)TiO3, and Pb(Zr,Ti)O3 by nebulized spray pyrolysis

Nebulized spray pyrolysis provides a good low‐temperature chemical route for preparing thin films of PbTiO3, (Pb0.9,La0.1)TiO3 and Pb(Zr0.52,Ti0.48)O3. The films are a‐ or c‐ axis oriented, with spherical grains of ∼30 nm and give satisfactory P‐E hysteresis loops.

Hopping conduction in charge-ordered rare-earth manganates Ln1−xCaxMnO3 (Ln=rare earth)

Abstract Electrical resistivity behavior of single crystals as well as polycrystalline pellets of rare earth manganates has been investigated below the charge-ordering temperatures to understand the mechanism of conduction. The resistivity of both the single- and polycrystalline samples of Gd0.5Ca0.5MnO3 and Nd0.5Ca0.5MnO3 obey the T−1/4 law, characteristic of variable range hopping. A similar dependence is found in the hole-doped Pr0.6Ca0.4MnO3 as well, but the data of the electron-doped Pr0.4Ca0.6MnO3 do not seem to obey any T−1/n law satisfactorily. AC conductivity measurements also reflect the unusual nature of the electron-doped composition.

Electrical properties of ferroelectric YMnO3 films deposited on n-type Si(111) substrates

YMnO 3 thin films were grown on an n-type Si substrate by nebulized spray pyrolysis in the metal-ferroelectric-semiconductor (MFS) configuration. The capacitance-voltage characteristics of the film in the MFS structure exhibit hysteretic behaviour consistent with the polarization charge switching direction, with the memory window decreasing with increase in temperature. The density of the interface states decreases with increasing annealing temperature. Mapping of the silicon energy band gap with the interface states has been carried out. The leakage current, measured in the accumulation region, is lower in well-crystallized thin films and obeys a space-charge limited conduction mechanism. The calculated activation energy from the dc leakage current characteristics of the Arrhenius plot reveals that the activation energy corresponds to oxygen vacancy motion.

Light element ceramics

An overview of a few structurally important light element ceramics is presented. Included in the overview are silicon nitride, sialon, aluminium nitride, boron nitride, boron carbide and silicon carbide. Methods of preparation, characterization and industrial applications of these ceramics are summarized. Mechanical properties, industrial production techniques and principal uses of these ceramics are emphasized.