Study of non-centrosymmetric to centrosymmetric structural transformation in Zr-doped Barium Titanate

Non-centrosymmetric to centrosymmetric structural transformation of BaZrxTi1-xO3 (x = 0, 0.05, 0.1, 0.3) as prepared by soilid state reaction was investigated from X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), pair distribution function (PDF) and Raman spectra. Tetragonal BaTiO3 transformed to orthorhombic phase for lower Zr concentration (x = 0.05) and changed to tetragonal to cubic with increasing Zr concentration at room temperature. Dielectric constant changed with the addition of Zr due to the change in local atomic arrangement and achieved highest value 1444 for mole fraction x = 0.1. Change occurred in the intensity for the first Ti-O pair in the PDF pattern due to the incorporation Zr in barium titanate lattice. An extra shoulder due to addition of Zr for the cubic phase of BZT has appeared at 5.64 angstrom in the PDF pattern. Structural and electrical properties of BZT were influenced by additions of Zr due to the change in local atomic arrangement

Investigation of local structure and phase transformation in Ce-doped barium titanate and correlation with electrical properties

BaTiO3-based materials are used as the replacement for lead-based perovskite materials for its wide dielectric applications. But the substitution of different doping elements in pure BaTiO3 drastically affects the microstructure, phase transition behavior and electrical properties. In the present work, local structure, phase transformation and dielectric behavior of BaCexTi1-xO3 (BCT) ceramics were studied for compositions x = 0.02, 0.05 and 0.1. A diffuse phase transition from orthorhombic to cubic via tetragonal in BCT with increasing Ce content was observed. An increase in particle size with Ce doping concentration was observed in FESEM images. Spherical and cuboid-shaped particle in the order of 80-150 nm was observed in transmission electron microscopic (TEM) images. RAMAN spectra confirm the tetragonal to cubic phase transition. Local structural and phase transformation behavior was obtained from laboratory-based PDF and XRD, respectively. Change in PDF was observed due to an increase in Ce doping. Dielectric properties decreased for Ce mole fraction of x = 0.1

Use of high temperature X-ray diffraction and pair distribution function for the study of carbonation characteristics of Barium Titanate at nanoscale

Barium titanate (BT) is extensively used in electronic industries for its high dielectric constant. However, the dielectric properties of BT significantly change due to carbonation at nanoscale. Commercially available tetragonal BT powder was milled to study the local atomic distribution and phase transformation behaviour with temperature. Nano BT powder was prepared by the high energy ball milling (90 h) from its bulk counterpart. It was carbonated when it was exposed to open atmosphere. The milled BT sample was characterised by high temperature X-ray diffraction (HT-XRD), pair distribution function (PDF) and transmission electron microscope (TEM). Local atomic distribution was obtained from PDF analysis. The peak due to C-O and Ba-C pair distance were observed from PDF for 90 h milled carbonated BT. TEM analysis revealed that particle diameter was in the range of 15-50 nm. How the phase of nano BT ceramics transformed with temperature was strudied. It was observed that orthorhombic BT transformed into tetragonal and cubic phase via the monoclinic phase during heating at 900 degrees C. Coexistence of multi phases of BT was also observed from HT-XRD. BaCO3 disappeared at high temperature

Trapped Exciton-Enhanced Response of n-TiO2(110)/p-Si(111) Nanostructures as Photodetectors

A p-type Si(111)/n-TiO2(110) heterojunction photodetector device has been fabricated for broad spectral range detection. An environmentally friendly NaCl assisted hydrothermal route was employed for synthesizing an n-type TiO2(110) hierarchical nanostructure powder. A 1 mu m thick film of TiO2 was then deposited by spin coating on the top of p-type Si(111). The role of NaCl in tuning both anionic (oxygen vacancy) and cationic (Ti mono- and divacancy, Ti interstitials) defects has been investigated. The vacancies posed a significant effect on photoresponse and junction characteristics of the device, viz., dark current, barrier height, photosensitivity, detectivity, and photoresponse gain. The TiO2 n-type layer fabricated at higher NaCl concentrations has been found to exhibit maximum responsivity of similar to 550 A/W, gain of similar to 2.00, specific detectivity of similar to 1.27 x 1011 Jones, and fast response and recovery times of 38 and 43 ms, respectively. The device has been highly repeatable (for 12 cycles) with a stability of 60 days. These have been ascribed to the exciton, formed at the bridged oxygen adjacent to the Ti vacancy at the (110) surface. We have also resolved that the charge carrier-phonon interaction facilitates exciton stabilization, while the charge transfer across the interface follows the adiabatic process. To explain the variation of device performance with defects, a mathematical model has been proposed to correlate the device responsivity to the different vacancies