(Ba,Sr)TiO3 (BST) thin films grown by chemical vapor deposition and with platinum (Pt) top and bottom electrodes have been characterized with respect to the leakage current as a function of temperature and applied voltage. The data can be interpreted via a thermionic emission model. The Schottky approximation accounts for superohmic behavior at higher fields, but the barrier lowering is stronger than expected from this theory. While the leakage mechanism is comparable to SrTiO3 thin films prepared by chemical solution deposition, the absolute values of the leakage current are significantly lower for the metalorganic chemical vapor deposition (MOCVD) prepared BST film. This is presumably due to a more homogeneous microstructure of the latter and may also be due to different electrode processing. The influence of the film thickness on the leakage in combination with additional findings is used to discuss the field distribution in the films under a dc voltage stress.

The influence of the electrodes on the dielectric behavior and especially on the leakage behavior of SrTiO3 thin films was investigated by impedance analysis. Based on measurements on thin films with different electrode materials the work function of these materials was found to determine the leakage currents. The main conduction mechanism is thermionic emission of electrons from the cathode into the SrTiO3 thin film. The current–voltage characteristics are influenced by the Schottky effect.

No abstract

Bulk specimens of the easy glass-forming alloy Pd40Ni40P20 have been undercooled consistently into the glassy state at cooling rates as low as 10 K/min applying the melt-fluxing technique in boron trioxide. Due to this low cooling rate, heat capacity measurements could be performed in a commercial heat-flow differential calorimeter, covering for the first time the entire undercooling regime of a liquid metal from the melting temperature down to the glass transition temperature. Based on the measured specific heat data of the undercooled liquid and the crystalline state, the differences in the thermodynamic functions enthalpy, entropy, and Gibbs free energy are determined in dependence on temperature. The entropy balance yields a value of T0=500±5 K for the ideal glass transition temperature of this metallic system. The experimental values are compared to the corresponding thermodynamic functions, derived from commonly applied Gibbs free energy approximations for the undercooled liquid.

No abstract