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In this work, structural, dielectric, ferroelectric, and ferromagnetic properties of BaTi1–xFexO3 (0

Tetragonal lead titanate ceramics in nano particles forms were fabricated via sol-gel method. The gelation was achieved via mixing a solution of lead acetate, titanium isopropoxide in a solvent system of ethanol and acetylacetone. The gel was heated in a normal air oven at 120°C for 5 hours to get ceramic powder which was calcined at 600°C for two hours and cintered upto 1100°C. The calcined powder was characterized by X-ray diffraction XRD and SEM analysis. It has been observed that the particle size increases with temperature with a decrease in grain boundary area.

Thin films of Ba1−xLaxTiO3 on platinum substrates were synthesized using the sol–gel method for x values of 0.0, 0.03, 0.05, and 0.10, and the effect of trivalent La3+ substitution on the structural and dielectric properties was studied. Using X-ray diffraction, structural analysis of these compositions revealed a slight increase in the tetragonal distortion of the unit cell with increase in La content. Accordingly, an increase in the tetragonal to cubic transition temperature TT/C was detected by temperature-dependent Raman spectroscopy in the range of 70–500 K. Unlike the results from Raman scattering for the La-doped BaTiO3 films, the dielectric measurements showed broad and diffused dielectric maxima, making the estimation of the transition temperature merely qualitative. Copyright © 2006 John Wiley & Sons, Ltd.

We have studied the lattice vibrational modes of Zr-substituted Bi4Ti3O12 ceramics using micro-Raman spectroscopy. Replacement of Zr at the Ti site in the perovskite block is found from the increase in the lattice parameters as a function of Zr contents. Combined X-ray diffraction patterns and Raman analysis suggested less than 40 mole% Zr solubility in Bi4Ti3O12. At 40 mole% of Zr substitution or above, the unreacted monoclinic-phase ZrO2 is observed in the X-ray diffraction patterns and the Raman spectra. The incorporation of Zr in Bi4Ti3O12 reduces the soft mode wavenumber and the transition temperature. Moreover, temperature dependent studies confirmed the ferroelectric to paraelectric transition in Bi4Ti3O12 at about 675 °C. On increasing the Zr content up to 40% on the Ti sites of Bi4Ti3O12, a systematic decrease in the phase transition temperature from 675 to 630 °C was observed. Copyright © 2007 John Wiley & Sons, Ltd.

Powder compacts of TiO2 and ZrO2 were prepared from their suspensions in water at different pH values, and micro-Raman spectroscopy was used to reveal the degree of mixing in each of them, with different sizes of the focused laser spot. The change in laser intensity and particle-size distributions led to a slight variation in the average composition, as determined using three different probe sizes. The Raman-estimated volume fractions of each constituent indicated that the aqueous suspensions in which the powders were well dispersed produced the most-uniform mixing. Powders that were flocculated in suspensions before mixing also resulted in a good mixture. The most-nonuniform mixing was observed when, in the individual suspensions, one of the constituents was dispersed and the other was flocculated. These results indicated that Raman spectroscopy can be useful for the rapid determination of the degree of mixing in powder mixtures.

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.

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 Ω cm. The resistivity of ZnO films decreased and remained in the range of 0.27–0.32 Ω 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.

A Raman spectroscopic study was performed on a Pb(Zn1/3Nb2/3)0.915Ti0.085O3 crystal to study the ordered nano-regions. The variation of the Raman spectra with temperature in the range from −200 to 1000°C clearly exhibited a rhombohedral–tetragonal transition at about 75°C followed by a tetragonal–cubic transition at about 175°C. The polarization behavior of the 777 cm−1 octahedral mode suggested the existence of Fm3m nano-ordered regions in Pm3m cubic symmetry. Thermal switching of nano-region polarization was observed above 388°C as the thermal energy became greater than the activation energy of nano-clusters and resulted in a decrease in the polarized intensity of the 777 cm−1 mode. However, both the 51 and 777 cm−1 modes were observed up to 1000°C. Copyright © 2003 John Wiley & Sons, Ltd.

Sol-gel derived Pb0.85La0.15TiO3 thin films were deposited on Pt, Pt/Si, RuO2/Pt/Si and RuO2/Si bottom electrodes. The structural and microstructural characteristics of the films were studied using X-ray diffraction and atomic force microscopy techniques. Dielectric, ferroelectric and leakage current characteristics were evaluated and depth profile Auger electron spectroscopy was used to obtain direct evidence for reactivity and compositional changes at the film/electrode interface and determine their effect on the ferroelectric and dielectric properties of films. Films deposited on Pt electrode showed a relatively higher dielectric constant of approximately 1300, while the films on RuO2 exhibited lower dielectric constant of only 470. J-t characteristics with leak-age current of approximately 10(-8) A/cm(2) under low biasing field (10 kV/cm) was observed for the films under study. The steady state field dependent de conductivity was examined by the measurement of J-E characteristics. At very low fields (< 30 kV/cm) films followed ohmic behavior and was fitted with a space-charge-limited conduction mechanism in the intermediate fields (30-60 kV/cm). The on-set voltage for the non-linearity was considered as V-TFL using which, the trap concentration estimated for films on RuO2/Si electrode was 1.23 X 10(17) cm(-3). Observed current characteristics have been correlated with large interfacial resistance at the film-electrode boundary. In the case of RuO2 bottom electrodes, the dielectric and ferroelectric properties are correlated with the electrode characteristics and Si diffusion at the film-electrode interface.

Single-phase (Nb2O5)1−x(TiO2)x ceramics were prepared for x = 0.00, 0.05, 0.08 and 0.11 compositions using a solid-state reaction technique. The effect of TiO2 substitution on the vibrational and phase transition behavior of Nb2O5 was studied using the micro-Raman scattering technique and compared with similar results on Ta2O5. The external modes resulting from interaction among various polyhedra were observed and vibrational changes were studied in the temperature range −200 to 1100°C. An increase in structural disorder was reflected in the Raman spectra with increasing TiO2 content in both Nb2O5 and Ta2O5. Ta2O5 shows a phase transition at about 300°C . However, a low-temperature phase transition was observed about 50°C from (Nb2O5)1−x(TiO2)x compositions. Copyright © 2002 John Wiley & Sons, Ltd.

Raman spectroscopy has been utilized to investigate the Sr-substitution, stress/strain, and grain size effects in Ba 1 m x Sr x TiO 3 ceramics. Ceramic samples were prepared for x = 0.00, 0.10, 0.30, and 0.35 compositions using a solid-state reaction technique. Single-phase perovskite structure of the ceramics was identified using the X-ray diffraction technique. A uniform incorporation of Sr in BaTiO 3 lattice was established from the identical Raman spectra in each ceramic. The tetragonal to cubic transition temperature was found to decrease linearly from 430 K to 280 K with increasing Sr-content from x = 0.00 to x = 0.35. No mechanical stresses or grain size effects were identified in these compositions, which indicated the stress free nature and the larger grain size of the material.

This paper provides a review of a systematic micro-Raman scattering study on various lead- and barium-based ABO3 perovskites (A = Pb, La, Ba, Sr, Ce, Gd, Nd and B = Ti, Zr), Aurivillius-type Bi-layered compounds (SrBi2Ta2O9, Bi4Ti3O12) and their solid solutions useful in a broad range of device applications. Various factors that influence the material properties such as particle size, stresses, stoichiometry, compositional homogeneity and their effects on phase transition were investigated. The processing conditions, A- and B-site substitution, size-dependent Raman spectra and the structure–property correlations are discussed in the bulk, thin film and nano-crystalline forms of these materials. A film thickness dependence stress study on lead titanate (PT) and lead zirconate titanate (PZT) films indicated that the nature of stress depends strongly on the lattice parameters of the film and substrate. The size effect was found to decrease the ferroelectric transition temperature in lead-based perovskite materials. Both ionic charge and radii induced changes in the Raman spectra of A- and B-site substituted perovskites and layered compounds were studied. A-site substitution in strontium bismuth tantalite (SBT) was found to induce a relatively linear variation of transition temperature compared with the B-site substituted SBT. Raman spectra of layered compounds and their solid solutions exhibited a strong dependence on dopants resulting in structural modifications. Copyright © 2002 John Wiley & Sons, Ltd.

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.

La-graded heterostructure films were prepared by sol-gel technique on platinum substrates and electrical properties of these films were compared with those of conventional thin films of similar compositions. X-ray diffraction results indicate the pure perovskite polycrystalline structure of these films. Atomic Force Microscopy analysis revealed a finer grain size and relatively lower surface roughness. Relatively higher values of Pm and Pr (69 and 38 ?C cm?2, respectively) and excellent dielectric properties with lower loss (K=1900, tan ?=0.035 at 100 kHz) were observed for La-graded heterostructure films. Also lower leakage current density (not, vert, similar2.5 nA cm?2) and a higher onset field (not, vert, similar50 kV cm?1) of space charge conduction indicated higher breakdown strength and good leakage current characteristics. The ac electric field dependence of the permittivity at sub-switching fields was analyzed in the framework of the Rayleigh dynamics of domain walls. The estimated irreversible domain wall displacement contribution to the total dielectric permittivity was 17 and 9% for conventional 15 at.% La doped PbTiO3 and La-graded heterostructure films, respectively. The improved dielectric and polarization behavior of La-graded heterostructure films may be attributed to homogenous dopant distribution compared to the conventional 15 at.% La doped PbTiO3 films.

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...

Ferroelectric memory was observed in {1- x SrBi 2 Ta 2 O 9 - x Bi 3 TiTaO 9 } material for the composition x =0.3. Thus, there is interest in the investigation of detailed properties of this material system. We report on the structural and electrical properties of this material system using X-ray diffraction, Raman spectroscopy, impedance spectroscopy, and ferroelectric measurements. These studies suggest that high quality powder and thin films could be prepared for all compositions by a chemical solution route at the temperature ranging from 650 to 750°C. Ferroelectric response was also observed in thin film (for x =0.5) and pellet (for x =0.0) samples.

Zn1–xMgxO is an important material for optoelectronic devices. We synthesized this material using a solution-based route. We investigated in detail the structural behavior of this material system using x-ray diffraction and Raman spectroscopy. Mg substitution up to x ≈ 0.10 does not change the crystal structure, as revealed by x-ray diffraction and Raman spectroscopic studies. This synthesis route is also suitable to prepare thin films by spin coating with the possibility of p and n doping.

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...

Tantalum pentoxide (Ta 2 O 5 ) is promising for coating and piezoelectric applications and has been considered as the dielectric gate material for the next generation of memory devices. In this work, TiO 2 -doped Ta 2 O 5 crystals were prepared using the laser-heated pedestal growth technique, as grown specimens were found to crystallize in monoclinic phase at room temperature. The structural modifications in these crystals resulting from variation of TiO 2 composition (0–11%) and temperature (−248–900°C) were studied using Raman spectroscopy. The low frequency external modes ( v −1 ) that originate from the interaction between TaO 5−2 n n /Ta 6 O +6 12 clusters/polyhedra exhibit a strong compositional and temperature dependence in terms of their intensity and frequency variations. The Raman spectral evolutions suggested a monoclinic to orthorhombic structural phase transition at about 327, 397, 487, and 577°C for 0, 5, 8, and 11% TiO 2 -doped Ta 2 O 5 , respectively.

We have studied the effect of rare earth dopants (Nd, Gd and Ce) on the phase formation behavior and electrical properties of sol-gel derived Pb1.05(Zr0.53Ti0.47)O3 thin films. In all these films the perovskite phase is obtained up to 5 at% doping and beyond that pyrochlore phase was found to coexist with the perovskite phase. Ce and Gd doping(1-2 at%) exhibited improved ferroelectric and dielectric properties as compared to the undoped PZT films. Nd doping (2 at%) was found to be effective to increase the retained switchable polarization of undoped PZT from 63% to 84%. The transition temperature of undoped PZT film was found to be reduced with Nd doping. The Nd doped films also exhibited typical relaxor behavior and a diffuse phase transition, characteristic of the relaxor material. Introduction of Nd into the PZT lattice probably introduces disorder in the B site of ABO3 lattice which causes the observed relaxor behavior

Ferroelectric Pb0.90La0.15TiO3 (PLT15) thin films were deposited by sol-gel method on Pt, Pt/Si, ruthenium oxide (RuO2)/Si and RuO2/Pt/Si bottom electrodes. X-ray diffraction, and micro-Raman spectroscopy techniques were used for structural characterization of these films. PLT15 films deposited on RuO2 electrodes show (100) preferred orientation of growth and result in larger crystallites. Films on Pt electrode exhibited higher dielectric constant (1300 at 100 kHz) and high values of Pm, Pr values, 68 and 46 μC/cm2 respectively. AC field dependence of dielectric permittivity at sub-switching fields was fitted using the Rayleigh law. The reversible polarization components estimated from the CV and quasi-static hysteresis measurements for films on Pt/Si (24%), was larger than that of Pt (11%) bottom electrodes. The observed results were correlated with the domain wall pinning at the disturbed film-electrode interface.

Sr1−x Ba x Bi2TaNbO9 materials have been synthesized using a chemical solution route. Detailed x-ray diffraction and Raman spectroscopic studies indicates the formation of complete solid solutions for all compositions (x = 0.0 to 1.00) in Sr1−x Ba x Bi2TaNbO9. Thin films were deposited by spin coating. Optical transmission of the film deposited on quartz disk showed the typical interference effect of optical thin films. Ferroelectric polarization on Sr0.5Ba05Bi2TaNbO9 film deposited on Pt substrate and annealed at 700 °C, was measured to be 13.5 μC/cm2.

In the present work the process methodology was optimized to synthesize highly textured (100) BST(50/50) and BST(60/40) thin films on single crystalline lanthanum aluminate substrates. These films were characterized in terms of their phase formation behavior, microstructure evolution and dielectric properties. We have also fabricated eight coupled micro-strip phase shifters (CMPS). An insertion loss of 8.43 dB, phase shift in the order of 320° (20–340V) and κ factor ∼38.0 was achieved in the BST(60/40) films.

Superior battery materials LiAlxCo1−xO2 (x = 0.0, 0.1, 0.3, 0.5, and 0.7) were synthesized using a solution-based route at various sintering temperatures (450–800 °C). In this communication, we report on the use of Raman spectroscopy to study effect of composition and sintering temperature on the resulting material. The phase evolutions in LiAlxCo1−xO2 compositions were studied using micro-Raman spectroscopy and a phase diagram is proposed based on the observations. For less Al content, the low-temperature phases of LiAlxCo1−xO2 showed Raman spectra corresponding to a monoclinic (space group C2/m) structure, while a low-temperature spinel (space group Fd3m) phase was observed for 50% or more Al in these compounds. All these compositions exhibited a layered hexagonal (space group R3m) structure when sintered above 700 °C. Raman spectra also revealed residual Co3O4 in the low-temperature forms of LiCoO2 and LiA10.01Co0.9O2.

Bismuth-based layered and perovskite tantalates, titanates and niobates have received special attention as ferroelectric and dielectric materials. Sr 1-x Ba x Bi 2 Ta 2 O 9 (x = 0.0, 0.2, 0.5, 0.7, and 1) were synthesized using a chemical solution route. As revealed by X-ray diffraction studies, they make a complete solid solution for all values of x. Thin films were deposited by spin coating. Stoichiometric thin films were achieved on quartz and stainless steel substrates at a process temperature below 700°C. Films were also characterized by Raman and impedance spectroscopy. The ferroelectric memory has been measured with Pr 27 μm/cm 2 on the Sr 0.3 Ba 0.7 Bi 2 Ta 2 O 9 film deposited on a stainless steel substrate and annealed at 650°C.

Bulk (Ta2O5)1−x(TiO2)x ceramics for x=0.05, 0.08, and 0.11 were prepared by the conventional solid state reaction technique and the temperature dependent Raman scattering in the range 70–1173 K was used to study the structural transformations in them. The lowest frequency phonon modes, at about 35–38 cm−1, in these ceramics were assigned as Ta–Ti vibrations originating from the interaction between TiO6 octahedra and TaOn5−2n or Ta6O12+6 clusters. Raman spectra exhibited a softening of this mode with increasing temperature, followed by a structural transformation. A structural transition from triclinic to monoclinic phase was observed in the ceramics at about 360, 450, and 540°C for compositions x=0.05, 0.08, and 0.11, respectively.

Due to its endurance to ferroelectric fatigue, SrBi2Ta2O9 (SBT) has been extensively investigated. We report here the synthesis of Sr1−xBaxBi2Ta2O9 (x = 0.0, 0.1, 0.5, 1.0) using a solution-based route. The precursors used in this work were the salts of strontium, barium, bismuth, and tantalum ethoxide. X-ray diffraction and Raman spectroscopic studies indicated the formation of complete solid solution system for Sr1−xBaxBi2Ta2O9. This material system may provide interesting properties relevant to microwave tuning and ferroelectric memory applications, which are under investigation.

High dielectric constant (Ta2O5)1−x(TiO2)x ceramics for x=0.00, 0.05, 0.08, and 0.11 were prepared and studied utilizing micro-Raman scattering and x-ray diffraction techniques. The modification in the lowest frequency phonon mode of pure Ta2O5 with increasing TiO2 content in these ceramics was assigned as Ta–Ti vibrations originating from the interaction between TiO6 octahedra and TaOn5-2n or Ta6O12+6 clusters. Raman spectra, in the range −200–900 °C, reveal a softening of this mode with increasing temperature followed by a structural transformation. A triclinic to monoclinic phase (Hmon′) transition was observed at about 300, 360, 450, and 540 °C for x=0.00, 0.05, 0.08, and 0.11, respectively. It was also found that reannealing at 1150 °C for 12 h transforms these ceramics from triclinic to a metastable monoclinic phase Hmon, which was found to be an irreversible process.

Tungsten bronze Sr0.5Ba0.5Nb2O6 nano-powders and thin films on platinum, Si(100), and sapphire substrates were prepared by the sol-gel route and characterized by x-ray diffraction and micro-Raman scattering techniques. The transparent and crack-free films crystallized into an orthorhombic phase at 700°C. Annealing of these films at higher temperature (∼ 750°C) for longer time yielded a mixture of ferroelectric tetragonal and a non ferroelectric orthorhombic phase. As a result, in some discrete regions of the films we could record well saturated hysteresis loops with reasonably good fatigue characteristics. Both the films and powders were completely transformed into a ferroelectric tetragonal tungsten bronze structure when annealed at 1100°C for 12 hours.

We have used Raman spectroscopy to investigate thin films of ferroelectric (SrBi2Ta2O9)x(Bi3TiNbO9)1−x layered structures and to compare them with the corresponding bulk materials. Various compositions, with x ' 0.0, 0.2, 0.4, 0.6, 0.8, and 1.0, were prepared by metal organic solution deposition method on Pt/TiO2/SiO2/Si substrates. A topographic micro-Raman study revealed very homogeneous films at each composition. The Raman spectrum of x ' 0.0 film shows bands around 170, 232, 337, 522, 608, 677 and 832 cm−1, which indicates Bi3TiNbO9 formation. The evolution of the Raman bands with the inclusion of SBT material shows frequency shifts and a broadening of the bands due to the differences in mass between Sr and Bi in the A-sites, and Ta, Ti, and Nb in the B-sites A lower degree of crystallization was found in the films compared to the bulk due to the presence of stress in the films. Strong contributions from defects were also observed in the temperature-dependent Raman spectra.

Lanthanum doped lead titanate Pb1−x Lax Ti1−x/4 O3 fibers (x '0, 5 and 15 at%) were grown by sol-gel technique and characterized for their phase formation behavior and crystal structure. The precursor sol was concentrated upon heating at 100°C to make it spinnable and used for fiber drawing. For heat treatment, a two-step heating schedule was designed on the basis of DSC analysis of the as drawn fibers. X-ray diffraction analysis showed that the tetragonality of the Lead Titanate (PT) fibers reduces with La doping and the structure is changed to pseudocubic from tetragonal. MicroRaman Spectroscopy confirms these observations of change in crystal structure and distortion in the material due to La doping. Dense and elongated grains of about 1 μm diameter were observed at the surface and at the cross section of PT fibers. La doped fibers show a porous fracture surface and also the grain size reduces dramatically with the addition of La. Strain energy is believed to play a major role in the observed ...

Spin coated Pb1−xLaxTi1−x/4Q3 thin films (x ' 0.00, 0.05.…0.30) on (0001) sapphire were studied using x-ray diffraction, atomic force microscopy, and Raman scattering in order to investigate the phase formation, surface morphology, and the phase transition behavior in them. The x-ray and Raman scattering reveal a decrease in tetragonality with La substitution in lead titanate. Microscopy estimated surface roughness was also found to be decreasing with the La doping. Raman scattering, in the temperature range 75–783K, shows the transition temperature about 730, 680, 614, and 563 K for x'0.05, 0.10, 0.15, and 0.20 compositions, respectively. The diffuse nature of the ferroelectric phase transition owing to a short-range structural disorder in the paraelectric cubic phase and an increase in the diffuseness with La doping indicates the relaxor behavior and its relationship with the local disorder in these materials.

Lead zirconate titanate (PZT) thin films with composition Zr/Ti ∼ 0.53/0.47 were deposited by the sol-gel technique. The films were characterized in terms of its polarization relaxation, fatigue and imprint characteristics. We have found that the polarization relaxation is due to the presence of a depolarization field which increases dramatically with the rise in temperature. Improved fatigue performance was observed when the film was fatigued with higher frequency. The direction of imprint depends on the state of polarization. With the increase in net polarization, the trapped charge density at the film-electrode interface increases which leads to imprint characteristics. Also the imprint increases considerably with the rise in temperature. Finally, we have made an attempt to correlate simultaneously fatigue, polarization relaxation, and imprint characteristics with the presence of mobile charge defects (viz. Vo) and defect dipoles (viz. VPb – Vo) in the film.

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...

Pb1.05−xLax(Ti1−x/4)O3 (x = 0.00, 0.05, 0.1, 0.15, 0.20, 0.25 and 0.30) thin films were deposited on sapphire (0001) substrates by an acetic acid modified sol-gel technique. The films were characterized, using various techniques, in terms of their phase formation behavior, composition, microstructure and electrical characteristics. It was observed that the sol-gel derived films crystallize into the perovskite phase without any paraelectric cubic pyrochlore phase formation. For less than 15 at% lanthanum composition, the films show a tetragonal phase which transforms into a cubic phase for higher lanthanum content. The observed reduction of the tetragonal distortion with La addition is due to the pronounced shrinkage of the ‘c’ axis. X-ray photoelectron spectroscopy (XPS) was used to analyze the chemical composition. The XPS results are in excellent agreement with the nominal composition of the films. All films are extremely smooth, crack- and pinhole-free, and have a dense uniform microstructure....

Lead titanate thin films and fibers were prepared by sol-gel technique and the phase formation behavior, surface morphology and the effect of strain on the microstructural features of these samples was investigated. The x-ray and micro-Raman scattering results indicate the formation of the tetragonal perovskite phase in both films and fibers. The analysis of the Raman phonon modes reveals that the film is more stressed than the fibers. The variation of stress has been correlated to the microstructural features in these structures.

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.

Porous silicon layers (PSL) prepared by anodizing crystalline silicon are found to show an increased dark conductivity upon exposure to light and also upon fast cooling from high temperatures. These effects can be annealed out but cannot be reversed upon exposure to infrared light. Their decay with time, dependence on exposure times and temperatures have been studied in detail. Micro-Raman measurements on PSL showed the presence of a-Si : H which is suggested to be responsible for these effects.

The linear polarization dependence of the photoluminescence of Al0.08Ga0.92As single quantum well laser structure has been investigated for the incident light propagating parallel to the plane of the structure. The polarization dependent excitonic recombinations exhibit fully polarized behavior of heavy- and light-holes for in plane incident electric field vector. The rotation of excitation beam polarization by 90°, however, shows depolarized behavior of excitonic recombinations. The strain induced mixing of heavy- and light-hole valence band is also inferred in this excitation geometry.

A nominal well width (20 nm) of Al0.08Ga0.92As quantum well structure has been fabricated by molecular beam epitaxy technique with the aim of obtaining a lasing device. The temperature evolution of quantum well photoluminescence was studied in the range 10–300 K which shows excitons being trapped at the interfacial defects below 100 K. The linear polarization effects in the photoluminescence have been studied for the incident and collected light propagating parallel to the plane of the well layer. In a very careful study, the luminescence was found to be fully polarized for the incident electric vector parallel to well layers, while it showed depolarized behaviour for the incident electric vector perpendicular to the well layers. The earlier conclusions based on photoluminescence excitation and absorption studies of heavy- and light-hole emissions are supported. The 20 nm quantum well structure has been corroborated using scanning tunnelling microscopy.

By an extensive micro-Raman study, oval-defect-related morphological, compositional and carrier concentration inhomogeneities were studied in MBE-grown GaAs and epitaxial layers. It was found that the crystalline morphology changes from point to point in the same defect. Though the films remain in a rather good crystalline state, the defects are shown to induce stress/strain in these films. The carrier concentration at the oval defects was also found to be less than at the epitaxial layers.

The free carrier concentration at oval defects in silicon‐doped GaAs grown by molecular beam epitaxy has been studied on the basis of longitudinal‐optical (LO)‐phonon plasmon coupled mode frequency through Raman spectroscopy. The carrier concentration at the oval defects was found to be lower as compared to the defect‐free regions. The variations of surface depletion width with the concentration calculated from LO phonon intensities was also used to obtain the carrier concentration at the oval defects. Excellent agreement was found between the carrier concentrations obtained from these two methods.

We have prepared bamboo-shaped C–N nanotubes–polyethylene oxide (PEO) composite films by solution cast technique and investigated their structural/microstructural and electrical properties and developed a correlation between them. The formation of clean compartmentalized bamboo-shaped C–N nanotubes was confirmed by TEM. SEM investigations revealed a homogeneous dispersion of nanotubes in PEO matrix. Enhanced electrical conductivity was observed for the C–N nanotubes–PEO composites than bare PEO. The conductivity measurements on the C–N nanotubes–PEO composite films with ~20 wt % concentration of C–N nanotubes showed an increase of eight orders (~7.5 × 10−8 to 6.2 S cm−1) of magnitude in conductivity from bare PEO film. Raman spectra showed the stress-free nature of the composites and established the bonding of nanotubes with PEO, which resulted in the variation of Raman parameters. The Raman data of composites corroborate the findings of variation in electrical conductivity.