Biferroic YCrO3

YCrO3 which has a monoclinic structure, shows weak ferromagnetism below 140 K (TN) and a ferroelectric transition at 473 K accompanied by hysteresis. We have determined the structure and energetics of YCrO3 with ferromagnetic and antiferromagnetic ordering by means of first-principles density functional theory calculations, based on pseudopotentials and a plane wave basis. The non-centrosymmetric monoclinic structure is found to be lower in energy than the orthorhombic structure, supporting the biferroic nature of YCrO3.Comment: 16 pages including figure

Quantum phase transition in few-layer NbSe2_2 probed through quantized conductance fluctuations

We present the first observation of dynamically modulated quantum phase transition (QPT) between two distinct charge density wave (CDW) phases in 2-dimensional 2H-NbSe$_2$. There is recent spectroscopic evidence for the presence of these two quantum phases, but its evidence in bulk measurements remained elusive. We studied suspended, ultra-thin \nbse devices fabricated on piezoelectric substrates - with tunable flakes thickness, disorder level and strain. We find a surprising evolution of the conductance fluctuation spectra across the CDW temperature: the conductance fluctuates between two precise values, separated by a quantum of conductance. These quantized fluctuations disappear for disordered and on-substrate devices. With the help of mean-field calculations, these observations can be explained as to arise from dynamical phase transition between the two CDW states. To affirm this idea, we vary the lateral strain across the device via piezoelectric medium and map out the phase diagram near the quantum critical point (QCP). The results resolve a long-standing mystery of the anomalously large spectroscopic gap in NbSe$_2$

Synthesis and structural characterization of the antiferroelectric lead zirconate nanotubes by pulsed laser deposition

For the first time, a pulsed laser ablation deposition (PLD) method has been employed for the synthesis of antiferroelectric lead zirconate, PbZrO3, (PZ) nanotubes within the pores of anodic aluminum oxide (AAO) templates. The structure and morphology of fabricated PZ nanotubes were characterized by number of techniques, including scanning electron microscope (SEM), X-ray diffraction (XRD) and transmission electron microscope (TEM)analysis. After postannealing at 650 °C, the PZ nanotubes exhibited a polycrystalline microstructure, and X-ray diffraction studies revealed that they are of an orthorhombic distorted perovskite crystal structure. TEM analysis confirmed that the obtained PZ nanotubes are composed of nanoparticles in the range of 3-7 nm and the thickness of the wall of the nanotubes is around 10 nm

Deep level transient spectroscopy studies on BaTiO<SUB>3</SUB> and Ba<SUB>1-x</SUB>Ca<SUB>x</SUB>TiO<SUB>3</SUB> thin films deposited on Si substrates

Laser ablation grown BaTiO3 and Ba1-xCaxTiO3 thin films were studied in the metal-ferroelectric-semiconductor configuration by the deep level transient spectroscopy (DLTS) technique. The capture cross section, bulk and interface traps were determined from the DLTS technique. The distributions of calculated interface states were mapped with the silicon energy band gap for both the thin films. The interface states of the Ba1-xCaxTiO3 thin films were found to be higher than the BaTiO3 thin films. The substitution of Ca2+ into the Ba2+ sites of BaTiO3 results in a decreased lattice constant, thereby leading to shrinkage in the unit cell. This might be one of the reasons for the higher density of interface states present in Ba1-xCaxTiO3, as it leads to a large number of unsaturated bonds at the interface of Si substrate-thin films. The calculated capture cross section of the interface traps in both the BaTiO3 and Ba1-xCaxTiO3 thin films was very low in the range of 10-21 cm2

Fabrication, structural characterization, and formation mechanism of ferroelectric SrBi<SUB>2</SUB>Ta<SUB>2</SUB>O<SUB>9</SUB> nanotubes

A capillary-enforced template-based method has been applied to fabricate strontium bismuth tantalate (SrBi2Ta2O9, SBTO) nanotubes (diameter ~200 nm) by filling SBTO precursor solution into the nanochannels of porous anodic aluminum oxide (AAO) templates. X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM) equipped with Energy-dispersive X-ray spectroscopy (EDX) have been employed to characterize the morphology, structure, and composition of as-prepared nanotubes. XRD and selected-area electron diffraction (SAED) investigations demonstrated that postannealed (650 &#176; C for 1 h) SBTO nanotubes were polycrystalline with an orthorhombic perovskite crystal structure. The FE-SEM and TEM results showed that uniform length and diameter of SBTO nanotubes were obtained. The thickness of the SBTO nanotube walls was about 30 nm. High resolution TEM (HRTEM) analysis confirmed that the obtained SBTO nanotubes are made of randomly aligned nanoparticles 5-10 nm in size. EDX analysis demonstrated that stoichiometric SrBi2Ta2O9 was formed. The possible formation mechanism of SBTO nanotubes in the AAO template is discussed

Synthesis and studies of Pb<SUB>0.76</SUB>Ca<SUB>0.24</SUB>TiO<SUB>3</SUB> nanoparticles derived by sol-gel

Pb0.76Ca0.24TiO3 (PCT24) nanoparticles were synthesized by modified sol-gel method and characterized by a number of experimental techniques such as X-ray diffraction, TGA-DTA, FTIR and transmission electron microscopy equipped with energy-dispersive X-ray spectroscopy (EDX). X-ray diffraction (XRD) and selected-area electron diffraction (SAED) investigations demonstrated that the postannealed (650 &#176; C for 1 h) PCT24 nanoparticles have tetragonal perovskite crystal structure. TEM have been employed to characterize the morphology, structure and composition of the as prepared nanoparticles. Dielectric results indicates the evidence for relaxor type behavior while observed leaky ferroelectric loops may be because of the defects such as grain boundaries and the pores in the sample as the sample was not heated at higher temperature, to retain the nanosize dimension of the particles

Structural and electrical studies on Bi<SUB>2</SUB>VO<SUB>5.5</SUB>/Bi<SUB>4</SUB>Ti<SUB>3</SUB>O<SUB>12</SUB> multilayer thin films

The textured multilayer (ML) thin films of bismuth layered ferroelectric (FE) compounds, Bi2VO5.5 (BVO) and Bi4Ti3O12 (BTO) with different individual layer thicknesses were fabricated via pulsed laser deposition technique on Pt(111)/TiO2/SiO2/Si substrates. X-ray diffraction studies confirmed that BVO and BTO retained their respective crystal structures in these multilayer (ML) thin films. The atomic force microscopy and scanning electron microscopy studies showed smooth and dense microstructures. The polarization hysteresis (P-E) studies on a representative (BVBT30) ML thin film at 300 K confirmed the remnant polarization (2P r ) and coercive field (E c ) to be ~20 &#181; C/cm2 and 250 kV/cm, respectively. The value of P r obtained was greater than that of the single layer thin film of BVO (P r ~5.6 &#181; C/cm2). The room temperature dielectric constant (&#949; r') and the loss (D) for BVBT30 ML measured at 100 kHz were 170 and 0.01, respectively. The frequency and temperature dependent dielectric constant, impedance, modulus and ac conductivity of these ML thin films were studied as a function of frequency (100 Hz-1 MHz) in the 25-300 &#176; C temperature range. Two distinct electrical responses were observed in these films, which were attributed to the grain effects at low temperatures and grain boundary effects at higher temperatures. The frequency dependent electrical conductivity was fitted well with the double power law which evidenced two different types of contributions to the conductivity; the low frequency conductivity being due to the short range translational hopping and the high frequency conductivity was due to the localized or reorientational hopping

Fabrication and characterization of crystalline cubic bismuth zinc niobate pyrochlore (Bi<SUB>1.5</SUB>ZnNb<SUB>1.5</SUB>O<SUB>7</SUB>) nanoparticles derived by sol-gel

Here, we report the fabrication and characterization of crystalline cubic bismuth zinc niobate pyrochlore, Bi1.5ZnNb1.5O7, (BZN) nanoparticles. A novel sol-gel method is used for the synthesis of air-stable and precipitate-free diol-based sols of BZN which was dried at 150&#176;C and partially calcined at 350 &#176; C/1 h to decompose organics and bring down the free energy barrier for crystallization. Annealed at 450-700 &#176; C/1 h, BZN powder exhibited nanocrystalline morphology. The average BZN nanoparticle size were about 6, 60 and 85 nm for the samples annealed at 450, 600 and 700 &#176; C/1 h, respectively as observed by transmission electron microscope (TEM). The crystallinity and phase formation of the as synthesized nanoparticles were confirmed by the selected-area electron diffraction (SAED), X-ray diffraction (XRD) and high resolution TEM (HRTEM) analysis. Energy-dispersive X-ray spectroscopy (EDX) analysis demonstrated that stoichiometric Bi1.5ZnNb1.5O7 was formed

ZnO nanocrystalline thin films: a correlation of microstructural, optoelectronic properties

The compositional, structural, microstructural, dc electrical conductivity and optical properties of undoped zinc oxide films prepared by the sol-gel process using a spin-coating technique were investigated. The ZnO films were obtained by 5 cycle spin-coated and dried zinc oxide films followed by annealing in air at 600 &#176; C. The films deposited on the platinum coated silicon substrate were crystallized in a hexagonal wurtzite form. The energy-dispersive X-ray (EDX) spectrometry shows Zn and O elements in the products with an approximate molar ratio. TEM image of ZnO thin film shows that a grain of about 60-80 nm in size is really an aggregate of many small crystallites of around 10-20 nm. Electron diffraction pattern shows that the ZnO films exhibited hexagonal structure. The SEM micrograph showed that the films consist in nanocrystalline grains randomly distributed with voids in different regions. The dc conductivity found in the range of 10-5-10-6 (&#937; cm)-1. The optical study showed that the spectra for all samples give the transparency in the visible range