R. Naik

Slater model applied to polarization graded ferroelectrics

Ferroelectric thin films of BaxSr1−xTiO3 with compositional gradients normal to the growth surface have been formed by the successive deposition and annealing of films having step-variable Ba to Sr ratios. By suitably tailoring the magnitude and sense of the gradient in Ba to Sr ratio, directional potentials can be built into the structures yielding a new, but controllable, hysteresis phenomenon. Slater’s empirical model for ferroelectric materials has been extended to also describe thin films with polarization gradients normal to the growth surface, i.e., graded ferroelectric devices. This model accounts for several aspects of these structures, including: the broadness of the permittivity plots with temperature, the formation of a spontaneous potential upon oscillatory field excitation, offsets in the hysteresis graphs along the displacement axis with directions which are gradient dependent, and the electric field dependence of that offset.

Giant effective pyroelectric coefficients from graded ferroelectric devices

Effective pyroelectric coefficients as large as 5 μC/cm2 °C, with peak responsivities at approximately 50 °C, were obtained from compositionally graded barium strontium titanate ferroelectric thin film devices formed on silicon using unbalanced magnetron sputter deposition. These effective pyroelectric coefficients are nearly two orders of magnitude larger than those observed from conventional pyroelectric thin film ferroelectric detectors.

TEMPERATURE DEPENDENCE OF CONVENTIONAL AND EFFECTIVE PYROELECTRIC COEFFICIENTS FOR COMPOSITIONALLY GRADED BAXSR1-XTIO3 FILMS

Ferroelectric thin films (∼1.2 μm) of BaxSr1−xTiO3 with gradients in composition normal to the growth surface were formed on platinum substrates by metalorganic decomposition. Effective (pseudo) pyroelectric coefficients as large as 0.06 μC/cm2 K have been obtained from these active ferroelectric devices under the application of an ac field (charge pumping). In contrast, a value of only −0.003 μC/cm2 K has been measured for the conventional pyroelectric coefficient.

Theoretical and experimental evidence of enhanced ferromagnetism in Ba and Mn cosubstituted BiFeO3

Ba and Mn doped BiFeO3 prepared through the pyrolysis of xerogel precursors are characterized by powder x-ray diffraction, high resolution transmission electron microscopy, superconducting quantum interference device magnetometry, and polarization measurements. Structural studies by x-ray diffraction and transmission electron microscopy show a tetragonal lattice for Ba substituted BiFeO3 and a rhombohedral lattice for Mn substituted BiFeO3. A large ferromagnetic hysteresis loop is observed for Ba doped BiFeO3. Coexistence of distorted rhombohedral and tetragonal phases is observed in Ba and Mn codoped BiFeO3, where enhanced ferroelectric and ferromagnetic properties are produced by the internal strain. Density functional calculations are used to substantiate the results.

Ferromagnetism and spin-polarized charge carriers in In2 O3 thin films

We present evidence for spin-polarized charge carriers in

Growth of Cu films on hydrogen terminated Si(100) and Si(111) surfaces

{\text{In}}_{2}{\text{O}}_{3}

Optical and electrical properties of Al1−xInxN films grown by plasma source molecular-beam epitaxy

films. Both

Bandgap engineering by tuning particle size and crystallinity of SnO2-Fe2O3 nanocrystalline composite thin films

{\text{In}}_{2}{\text{O}}_{3}

Weak ferromagnetic ordering in Ca doped polycrystalline BiFeO3

and Cr doped

Stress-induced polarization-graded ferroelectrics

{\text{In}}_{2}{\text{O}}_{3}