P. S. Dobal

Micro-Raman scattering and dielectric investigations of phase transition behavior in the BaTiO3–BaZrO3 system

In this study, the phase transition behavior of the BaTiO3–BaZrO3 system was studied using micro-Raman scattering and dielectric measurement techniques. BaZrxTi1−xO3 ceramics were prepared for x=0.00, 0.05, 0.08, 0.15, 0.20, and 1.00 compositions using a solid-state reaction technique. A single-phase perovskite structure of the ceramics was identified by the x-ray diffraction technique. The basic phase transition temperatures in these compositions were studied in the temperature range of 70–575 K. The tetragonal to cubic transition temperature was found to decrease with increasing Zr content. The orthorhombic to tetragonal transition temperature that increases with an initial increase in Zr content merges with the tetragonal–cubic transition for x⩾0.15 compositions. Raman spectra of rhombohedral and orthorhombic phases could not be distinguished. Excellent agreement between the crystallographic transition temperatures obtained by both techniques suggested that Zr substituted octahedra were uniformly distr...

Investigations on solution derived aluminium doped zinc oxide thin films

Aluminium (Al) doped transparent zinc oxide thin films have been successfully grown on sapphire (0 0 0 1) substrates by an economical chemical solution deposition technique. These films were characterized in terms of their structural, optical, and electrical properties. Detailed XPS analysis of the O1s core level spectra has been carried out for the ZnO films annealed at different temperatures. Lower binding energy oxygen peak (O1) is related to ZnO bond, whereas higher binding energy peaks (O2 and O3) are related to the presence of OH and H2O species. Zn is bonded mainly to oxygen, however presence of metallic Zn was also detected by XPS. Decrease in O2 and O3 contents with the increase in annealing temperature has been correlated with the microstructure of the film. Higher annealing temperature was found to be effective to densify the film and thereby reduced the contents of the hydrated species. An optical transmittance 80/90% in the visible range and an optical band gap /3.25 eV was measured in case of undoped ZnO thin film. There is no significant change in band gap energy with Al doping. The resistivity of undoped ZnO was measured to be about 3.8 V cm. The resistivity of ZnO films decreased and remained in the range of 0.27/0.32 V cm for up to 4 at.% Al doping. Al doping content beyond 4 at.% was found to increase the resistivity of the films probably due to the segregation of aluminium as oxide resulting scattering of the electrons. # 2003 Elsevier B.V. All rights reserved.

Phase transition studies of sol–gel deposited barium zirconate titanate thin films

The present work was focused to investigate the phase transition behavior of sol–gel derived Ba(ZrxTi1−x)O3 (BZT) (0≤x≤0.40) thin films on platinum substrates for their possible applications in piezoelectric sensors and actuators. The phase transition behavior of these films was studied using micro-Raman spectroscopy in conjunction with the temperature dependent dielectric measurements. The spectra clearly indicate that the room temperature BZT films with Zr ≤0.05 were crystallized into tetragonal structure and above 15 at.% Zr substitution BZT thin films transformed into a disordered cubic structure. This disorder behavior became more pronounced for films with Zr>20 at.% with a plateau-type feature developing approximately 700 cm−1 and on cooling such films to the liquid nitrogen temperature no appreciable spectral changes were noticed. The dielectric properties of such films for Zr ≥25 at.% clearly indicated relaxor behavior. These environmentally safe (non-lead based) BZT films may have significant impact for several micro-electromechanical systems (MEMs) devices.

Large ferroelectric response in Bi4−xNdxTi3O12 films prepared by sol–gel process

Neodymium-substituted Bi4Ti3O12 (i.e., Bi4−xNdxTi3O12) were synthesized by sol–gel process for different compositions. Thin films were deposited on Pt (i.e., Pt/TiO2/SiO2/Si) substrate by spin coating. Materials were characterized by x-ray diffraction and Raman spectroscopy. This study indicates that the material makes a solid solution for the compositions: x=0.00, 0.26, 0.46, 0.75, 0.85, 1.00, and 2.00, where an Nd ion replaces the Bi site. The prominent effect of Nd substitution is observed in low-frequency Raman modes. Sol–gel derived thin films of Bi3.54Nd0.46Ti3O12 on a Pt substrate and postannealed at 700 ° C were tested for ferroelectric response which showed high remnant polarization (Pr=25 μC/cm2).

X-ray photoelectron spectroscopy and micro-Raman analysis of conductive RuO2 thin films

Ruthenium oxide (RuO2) was synthesized in thin film and powder forms using the solution chemistry technique. The oxide electrodes on Si substrates were characterized in terms of their structure, composition, stoichiometry, and conductivity. X-ray lattice parameter calculations and micro-Raman analysis revealed the rutile structure in the material. Both films and powders exhibited an unassigned Raman band at about 477 cm−1 in their Raman spectra. Performing peak frequency calculations for B2g and A1g modes of RuO2 using the rigid-ion model, which ruled out the possibility that this band originated from disorder induced symmetry, allowed silent mode. Based on the x-ray photoelectron spectroscopy (XPS) and temperature dependent Raman studies, this band was assigned to hydrated RuO2. XPS characterizations of our samples revealed minute surface contamination of oxygen and chlorine, probably due to the film preparation and high temperature deposition processes. Films with uniform microstructure, low surface rou...

Raman scattering study of a phase transition in tantalum pentoxide

Ta2O5 ceramics and crystals were prepared and analyzed using Raman spectroscopy in the temperature range 25–873 K. The low-energy phonon bands (ν < 100 cm−1) of Ta2O5 are assigned to external modes originating from the interaction between different Ta polyhedra and TaOn5 − 2n Ta6O126+ clusters. The temperature and polarization dependence of external modes suggests the existence of clusters in the material. A softening of the low-energy bands was observed with increasing temperature. The spectral evolutions show a soft mode-derived second-order monoclinic to orthorhombic phase transition at about 600 K in Ta2O5. Copyright

Studies on the structural, microstructural and optical properties of sol–gel derived lead lanthanum titanate thin films

Abstract The La modified lead titanate Pb 1− x La x Ti 1− x /4 O 3 (PLT) ( x =0.0, 0.05, 0.10, 0.15, 0.20, 0.25 and 0.30) thin films were deposited on sapphire (0001) substrates by the sol–gel process. The X-ray diffraction data and micro-Raman analysis show that with the increase in La content the crystal quality of the PLT films undergoes a tetragonal-to-cubic transformation. X-ray photoelectron spectroscopy analysis shows an excellent surface stoichiometry for all compositions under study. The optical properties of these films were investigated using both transmission and reflection spectra in the wavelength range of 200–900 nm. The appearance of interference fringes is an indication of the thickness uniformity of the film. The low value of extinction coefficient (in the order of 10 −2 ) as observed in our films is a qualitative indication of excellent surface smoothness of the films. Absorption coefficient ( α ) and the band-gap energy ( E g ) are obtained for undoped and La doped films with varying La concentrations. It has been found that the refractive index and packing fraction values decrease with La doping. Lanthanum doping was found to decrease the grain size of the films and improve the densification of individual grains. Increased La content lead to clusterification of smaller grains. The observed variation of band-gap energy with La doping has been correlated with the observed microstructure of these films.

Micro-Raman investigation of stress variations in lead titanate films on sapphire

Using the sol–gel method, PbTiO3 films of 21, 64, 128, 210, 310, and 420 nm thicknesses were obtained on (0001) sapphire. Raman scattering and x-ray diffraction techniques were used to study the correlation between the film thickness and the structural changes on these films. The Raman and x-ray intensities in 21 nm film were too weak to reveal any structural information, while all other films showed tetragonal structure. At room temperature, the variation of lowest E(1TO) phonon mode frequency with film thickness was observed due to compressive stresses in the films. The lattice parameters and the degree of a axis orientation values of tetragonal PbTiO3 have been evaluated as a function of film thickness. The changes in lattice parameters thus obtained were used to estimate the stress at each thickness. An excellent agreement was found between the stress values obtained using Raman and x-ray results. An exponential decrease in stress with increasing film thickness was observed because of the structural c...

Photoluminescence study of deep levels in Cr-doped ZnSe

Single crystals of intrinsic ZnSe were grown by the seeded physical vapor transport method and the diffusion doping was utilized to incorporate Cr in these crystals. The radiative recombinations in these samples with Cr concentration in the range 1.0–10.2×1019 cm−3 were studied by the steady state photoluminescence technique. It was found that the Cr deep centers inhibit the band-to-band emission in Cr-doped ZnSe. Except in undoped single crystals, no emission corresponding to the band-to-band transition was observed from any of the doped samples. Instead, the higher wavelength emissions associated with Cr deep levels were obtained. This capture of photoexcited carriers by deep centers was verified using different excitation wavelengths. The role of chromium impurities in nonradiative recombination processes was also evidenced from the sharp decreases in the deep level emission intensity with increasing Cr concentration.

Phase transition behavior of BaZrxTi1−xO3 ceramics

BaZrxTi1−xO3 ceramics were prepared for x = 0, 0.05, 0.08, 0.15 and 0.20 using a solid-state reaction technique. The evolution of the Raman spectra with temperature was used to study the variation of the basic phase transition temperatures of BaTiO3 in these compositions. The tetragonal to cubic transition temperature on heating was found to decrease with increasing Zr content. The orthorhombic to tetragonal transition temperature, which increases with initial increase in Zr content, merges with the tetragonal to cubic transition for x ≥ 0.15 compositions. These Raman results are in excellent agreement with those obtained from dielectric measurements. Copyright