Volume 88, Issue 10, 15 November 2000
Index of content:
- DIELECTRICS AND FERROELECTRICITY (PACS 77)
Influence of annealing temperature on ferroelectric properties of thin films prepared by off-axis radio frequency magnetron sputtering88(2000); http://dx.doi.org/10.1063/1.1317240View Description Hide Description
Ferroelectric (SBT) thin films were deposited on substrates using the off-axis radio frequency magnetronsputtering technique. X-ray diffraction and atomic force microscopy experiments showed that the crystallization of SBT thin films at >700 °C correlated with the formation of rod-like grains. Cross-sectional field emission scanning electron microscopy images revealed that the apparent thickness of SBT decreased while the thickness of Pt increased as the annealing temperature was increased. The apparent decrease in the thickness of SBT was attributed to crystallization and densification in the film whereas the apparent increase in Pt thickness was due to diffusion of Ti and Bi into the Pt layer. This diffusion at high annealing temperatures (800 °C and above) alters the Pt purity and degrades the Pt as the bottom electrode for the ferroelectric capacitor. Good insulating properties were obtained when the SBT film was annealed at 700 and 750 °C whereas higher leakage currents were observed at annealing temperatures >800 °C. A remnant polarization of 4.35 μC/cm2 and coercive field of 31.5 kV/cm were obtained for the SBT thin filmannealed at 750 °C with a leakage current density of
Dielectric, thermal, and mechanical properties of the semiorganic nonlinear optical crystal sodium p-nitrophenolate dihydrate88(2000); http://dx.doi.org/10.1063/1.1319651View Description Hide Description
Physical properties such as dielectric,specific heat,thermal expansion, and mechanical hardness have been measured for sodiump-nitrophenolate dihydrate single crystals. The dielectricmeasurements were made both as a function of frequency (in the range 15 kHz–10 MHz) and temperature (in the range 30–80 °C). For the range of frequencies measured the values were found to vary between 4.03 and 3.69 for 8.11 and 7.05 for and 5.71 and 5.36 for at room temperature, and piezoelectric resonances were observed at certain frequencies. The dielectricmeasurements made as a function of temperature did not exhibit any anomaly in the temperature range measured. The specific heat studies carried out for this compound showed ≈30% increase in with the temperature in the measured range. The thermal expansionmeasured as a function of temperature in the range 30–80 °C exhibited linear behavior and the average thermal expansion coefficients were found to be and The polar plots drawn for these coefficients were correlated with crystallographic features of the structure. The Vickers hardnessmeasurements, carried out along the three crystallographic axes, also exhibited anisotropy.
88(2000); http://dx.doi.org/10.1063/1.1322387View Description Hide Description
Ferroelectric (BLT) thin films were prepared on platinum coated silicon substrate by chemical solutiondeposition. The layered-perovskite phase was obtained by rapid thermal annealing the spin-on films at 650 or 700 °C for 180 s. Scanning electron micrographs showed uniform surfaces composed of spherical grains. The grain size increased with increasing annealing temperature. The remanent polarization and coercive field of 650 °C annealedfilm were 12.3 μC/cm2 and 48.9 kV/cm, respectively, and those of 700 °C annealedfilms were 18.2 μC/cm2 and 51.1 kV/cm. BLT thin films showed little polarization fatigue under 250 kV/cm bipolar cycling at 50 kHz, while fatigue properties deteriorated with decreasing cycling field and frequency. At various frequencies from 1 Hz to 50 kHz, nonvolatile polarization showed nearly no degradation over an initial period of cycling, then decayed logarithmically with switching cycles. The onset of logarithmic decay of was found to increase linearly with cycling frequency. The cycling field dependence of fatigue characteristics was interpreted in terms of competition of charge trapping which blocks the domain switching and field-assisted detrapping of charged defects which set the locked domains free. Frequency dependent fatigue properties were discussed on the basis of drift and aggregation of oxygen vacancies.