The electronic conduction through a Pr 0.7 Ca 0.3 MnO 3 thin film is investigated by measurements using dc and pulsed biases. Semiconducting Pr 0.7 Ca 0.3 MnO 3 films sandwiched by electrodes show both hysteretic and asymmetric behaviors in current-voltage characteristics. The observed conduction characteristics exhibit the spacecharge-limited-current effect, and the hysteretic behavior can be ascribed to a carrier trapping and detrapping of the trap sites in the manganite. The hysteresis induces a colossal electroresistance (CER) of more than 5000% at room temperature. The CER ratio is independent of the duration time of pulses from an infinite (dc) down to 150 ns, indicating that the carrier filling of all the traps can be completed within a short time.

To explore the possibility of large thermoelectric responses on the basis of d-electron orbital degeneracy, we investigated electrical and thermal transport properties of single crystals of electron-doped KTaO 3 . The electron-type carrier density (n) can be increased up to 1:4 Â 10 20 cm À3 (x ¼ 0:009) by partially substituting K with Ba in the form of K 1Àx Ba x TaO 3 . The power factor and dimensionless figure of merit at room temperature steeply increase with n, up to 14 mW cm À1 K À2 and 0.03 for x ¼ 0:009, respectively. This suggests that K 1Àx Ba x TaO 3 is a potential thermoelectric material, provided that n can be further increased.

No abstract

High-quality (K,Na)NbO3 thin films were successfully deposited on a (100) SrTiO3 (STO) substrate by pulsed laser deposition. High-density KNbO3 (KN), (K0.5Na0.5)NbO3 (KNN) and NaNbO3 (NN) ceramic targets were prepared by spark plasma sintering (SPS). The crystallographic analyses of the film were performed by conventional X-ray diffraction (XRD) analysis and rocking curve measurement. The XRD reciprocal space map was also measured to determine the lattice constants of the film and analyze the crystallographic relationship between the grown film and the STO substrate. The fluctuation change in the orientation of crystals in the grown film decreased and the smoothness of the film surface improved with increasing sodium content of the film. For the NN films, the full width at half maximum (FWHM) of the rocking curve was as small as 0.12°. The XRD reciprocal space map measurements showed that the lattices of the KN and KNN films relaxed on the STO substrate but the NN film was restricted to it.

Orientated NaNbO3 (NN) films were grown on SrRuO3/(001)SrTiO3 [SRO/(001)STO], SRO/(110)STO, and SRO/(111)STO substrates by pulsed laser deposition. Scanning electron microscopy images showed that the surface morphologies of the NN/SRO/(001)STO, NN/SRO/(110)STO, and NN/SRO/(111)STO took the form of a stepped structure, a striped pattern, and trigonal pyramidal-like structures, respectively. The dielectric and ferroelectric properties of the films were characterized. The NN/SRO/(110)STO film showed the lowest relative dielectric constant and the largest remanent polarization of 30.8 μC/cm2 among all films. These were interpreted as being due to the orientation direction of the NN film grown on (110)STO being parallel to the polarization direction of NN.

No abstract

High-quality NaNbO3 (NN) thin films were epitaxially grown on a (100)SrTiO3 substrate by pulsed-laser deposition. NN films with a flat surface morphology were obtained, when the films were grown slowly at high substrate temperatures, high oxygen partial pressures, and low laser energy densities. In order to characterize their dielectric properties, the NN films were epitaxially grown on (100)SrRuO3∥(100)SrTiO3 substrates. The relative dielectric constant, ε r, and dielectric loss, tan δ of the film were 252 and 0.03 at 1 kHz, respectively. When the temperature dependence of ε r was measured, ε r was found to suddenly increase at 377°C, which corresponds to the transition temperature of NN between the antiferroelectric and paraelectric phases. The P–E hysteresis loop of the NN films exhibited characteristic ferroelectric behavior.

We have fabricated epitaxial thin films of layered cobaltite AxCoO2 (A=Sr and Ca) on sapphire substrates by rf magnetron sputtering. The grown phase in the AxCoO2 films was found to be a monoclinic β-phase of primitive layered cobaltites and the epitaxial orientation of the film could be controlled by the surface plane of the substrates. The resistivity parallel to the CoO2 layers ρ‖ for the β-SrxCoO2 is as low as 2mΩcm at room temperature and shows metallic behavior. The ratio of perpendicular resistivity ρ⊥ to ρ‖ increases from 20 at room temperature to 90 at 3K. More isotropic nature was observed in the Seebeck coefficient. Parallel Seebeck coefficients S‖ of AxCoO2 are approximately 60μV∕K at room temperature and the perpendicular S⊥ are about half of S‖.