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We investigate the temperature dependent (83K ⩽ T ⩽ 523K) frequency shift of 2A1g and 1E2g phonon modes in the three dimensional topological insulator Bi2Se3, using Raman spectroscopy. The high quality single crystals of Bi2Se3 were grown using a modified Bridgman technique and characterized by Laue diffraction and high resolution transmission electron microscopy. A significant broadening in the line shape and red-shift in the frequencies were observed with increase in temperature. Polarized Raman scattering measurement shows a strong polarization effect of A1g and A2g phonon modes which confirms the good quality single crystals of Bi2Se3. Temperature co-efficient for A11g; E2g , and A21g modes was estimated to be -1.44 × 10-2, -1.94 ×10-2, and -1.95 ×10-2 cm-1/K, respectively. Our results shed light on anharmonic properties of Bi2Se3. [ABSTRACT FROM AUTHOR]

Antimony doped p-type ZnO films were grown on Al2O3 (0001) substrate by pulsed laser deposition. The structural properties of Zn1-xSbxO (3% and 5%) thin films were investigated by Raman scattering studies. The softening of local lattice due to the formation of (SbZn-2VZn) acceptor complexes was detected as the shift in E2high mode toward lower frequency side in ZnSbO thin films. Additional optical modes observed at 277, 333, 483, and 534 cm-1 are due to the breaking of translational symmetry in w-ZnO by Sb doping. The Zn-Sb related local vibrational mode was detected around 237 cm-1 in 5% Sb doped ZnO thin film. Room temperature Hall measurements exhibited low resistivity of 0.017 Ω cm, high hole concentration of 6.25×1018 cm-3, and mobility of 57.44 cm2/V s in the 5% Sb-doped ZnO thin film. [ABSTRACT FROM AUTHOR]

CuAlO2 thin films were grown on single crystalline sapphire substrates with c-axis orientation by rf sputtering method. The x-ray diffraction data indicate the formation of delafossite structure and tend to be oriented along (001). Temperature dependent Raman spectra of CuAlO2 thin films were measured from 80 to 1273 K, and we observed two optical modes at Eg (∼418 cm-1) and A1g(∼767 cm-1) showing anomalous frequency and linewidth shifts with temperature, which were interpreted as an experimental evidence of combined effect of lattice expansion and anharmonic phonon-phonon interaction in CuAlO2. At high temperature, polaronic state and change in effective mass due to lattice expansion also affect the frequency shift and the linewidth of the observed Raman modes. [ABSTRACT FROM AUTHOR]

Bismuth zinc niobate (Bi1.5Zn1.0Nb1.5O7) thin films were deposited on fused silica substrates by pulsed laser deposition. Its phase composition and microstructure were characterized by x-ray diffraction and atomic force microscopy. The as deposited films were amorphous and all of them were crystallized after a postdeposition annealing at 600 °C for 30 min in air. The crystallite size of the films was found to be varying between 31 and 60 nm with respect to the oxygen pressure in the deposition chamber. The films were found to be less oriented with the decreasing crystallite size. The films deposited under different oxygen pressures showed a microwave dielectric permittivity in between 98–124 and a loss tangent in between 0.005 and 0.007 over the X-band frequency range. From the Raman scattering data of the bulk and thin films, it was found that the Raman modes in thin films are relatively more intense and additional Raman modes were appearing in the films in the low frequency range, which reveal that the local symmetry in the films is different from that of the bulk. The variations in the microwave dielectric properties due to processing can be attributed to the change in the local symmetry of the film. [ABSTRACT FROM AUTHOR]

(PbZr0.53Ti0.47O3)(1-x)-(PbFe0.5Ta0.5O3)x, (PZTFT, x = 0, 0.1, 0.2, 0.3, 0.4, 1) ceramics were prepared by conventional solid state reaction route. X-ray diffraction patterns and Raman spectra revealed the formation of single phase tetragonal crystal structure at ambient temperature. With increase of Pb(Fe0.5Ta0.5)O3 (PFT) composition in PZTFT matrix significant enhancement in the grain size was observed where average grain sizes were in the range of 1-15 μm. Naturally designed PZTFT composites show higher dielectric constant than Pb(Zr0.53Ti0.47)O3 (PZT) but less than PFT. The ferroelectric (FE) to paraelectric (PE) phase transition temperature i.e. Curie temperature (Tc) shifted towards lower temperature side with increase in iron and tantalum compositions. Both polarization and magnetic moment were observed at room temperature in all PZTFT (x ≥ 0.2) composites suggesting multiferroic characteristic in these systems. Significant improvement of the ferroic properties were observed with increase of PFT concentration. [ABSTRACT FROM AUTHOR]

The magnetic properties of BiFeO3(BFO) - CoFe2O4(CFO) heterostructure thin films, grown on (100), (110) and (111) SrTiO3 (STO) substrates by employing pulsed laser deposition (PLD) method, have been studied. The XRD patterns of BFO-CFO multilayer thin films compared with the pure CFO and BFO thin films grown using under identical conditions evidenced that all peaks present correspond to CFO and BFO structure in two separate phases. Micro-Raman spectra analysis also reveals the presence of BFO and CFO in two separate phases in the heterostructures thin films. The anomalous enhancement in magnetization has been observed for BFO-CFO multilayer thin films, relative to pure BFO thin films in all three different orientations. The saturation magnetization for (100), (111) and (110) oriented BFO-CFO thin films are 44, 62 and 80 emu/cc suggesting that (110) is most preferable direction to achieve the magneto electric (ME) coupling effect. [ABSTRACT FROM AUTHOR]

BaTiO 3 /SrTiO 3 superlattices were grown on (001)MgO substrates by pulsed-laser-deposition technique. The thickness of each layer varied from 6 to 25 unit cells. Polarization-dependent Raman spectra confirmed tetragonal symmetry of the superlattices with the polar axis being normal to the layers. The observed optic modes in the superlattices showed intermediate frequencies between corresponding bulk BaTiO 3 and SrTiO 3 values, while the E( TO 1 ) soft mode exhibited upward shift due to significant two-dimensional clamping caused by the lattice mismatch of the constituting layers. The observed downward shift of the soft mode revealed relaxation of two-dimensional stresses with increasing the stacking periodicity of the superlattices. The excitation of folded transverse acoustic phonons in the Raman spectra due to the new periodicity of the Brillouin zone was revealed. The observed data are quantitatively explained by a folding of the corresponding acoustic branch. It is shown that micro-Raman spectroscopy provides determination of a spatial variation of the layer thickness in graded superlattices. [ABSTRACT FROM AUTHOR]

Raman spectra of epitaxal BiFeO3 thin films, grown on (111) SrTiO3 substrates, have been studied in temperature range 300-800 K. All four prominent A1-symmetry (81, 138, 170, and 214 cm-1) Raman modes show evolution with the temperature near the Néel temperature (TN), which is interpreted due to spin lattice coupling and it could be also linked with the structural instability originated by octahedral tilting near TN as reported by A. Palewicz et al., Acta Cryst B 63, 537 (2007). As another evidence of spin-phonon coupling, softening of the 214 cm-1 stretching mode is observed near and below the magnetic ordering temperature. [ABSTRACT FROM AUTHOR]

Abstract: We here report the structural and optical studies of Zn1−x−y Be x Mg y O (0≤ x ≤0.15; 0≤ y ≤0.20) powders and thin films. From the Rietveld refinement of the powder X-ray diffraction (XRD) patterns it was revealed that the value of ‘a’ lattice parameter remains almost unchanged whereas ‘c’ parameter reduces with Be and Mg co-doping in ZnO. The Zn-O bond length also decreases in co-doped samples. Raman studies of the pure ZnO powder showed all the characteristic peaks of the wurtzite hexagonal structure and with (Be, Mg) co-doping new modes appeared which can be attributed to arise as a result of substitution. The XRD of the films prepared from the powders using pulsed laser deposition (PLD) technique exhibited the preferential orientation and with increase in co-doping the (0002) peak also shifts to higher 2θ values suggesting the incorporation of Be/Mg at the Zn-site. From the UV–visible optical transmittance measurement it was noticed that the band gap of the pristine ZnO film is 3.3eV which enhanced up to 4.51eV for Zn0.7Be0.1Mg0.2O film which lies in the solar blind region and is very useful in the realization of deep UV detectors. [ABSTRACT FROM AUTHOR]

We investigate the temperature dependent (83K ⩽ T ⩽ 523K) frequency shift of 2A1g and 1E2g phonon modes in the three dimensional topological insulator Bi2Se3, using Raman spectroscopy. The high quality single crystals of Bi2Se3 were grown using a modified Bridgman technique and characterized by Laue diffraction and high resolution transmission electron microscopy. A significant broadening in the line shape and red-shift in the frequencies were observed with increase in temperature. Polarized Raman scattering measurement shows a strong polarization effect of A1g and A2g phonon modes which confirms the good quality single crystals of Bi2Se3. Temperature co-efficient for A11g; E2g , and A21g modes was estimated to be -1.44 × 10-2, -1.94 ×10-2, and -1.95 ×10-2 cm-1/K, respectively. Our results shed light on anharmonic properties of Bi2Se3. [ABSTRACT FROM AUTHOR]

Abstract: Monoclinic Bi2Zn2/3Nb4/3O7 (m-BZN) thin films were deposited by pulsed laser deposition on fused silica substrates at different oxygen pressures. Microwave dielectric and Raman scattering studies were systematically carried out on films that had been annealed at 600 °C after deposition. The dielectric constant of films changes in the range 56–71 due to varying the oxygen pressure during deposition. X-ray diffraction measurements indicate that the BZN thin films deposited at the oxygen pressure of 10 Pa have the best crystalline quality. Atomic force microscopy results show that the surface roughness of the m-BZN film increases with the increase of oxygen pressure. The anomalous change in two higher-frequency Ag modes appearing at 774 and with varying oxygen pressure also suggests a nonequivalent change in the oxygen octahedra around the Nb and Zn and is closely related to the microwave dielectric properties of the thin films. [Copyright &y& Elsevier]

Abstract: Raman scattering from one-magnon excitation has been observed for the first time in epitaxial BiFeO3 thin films grown on (111) SrTiO3 substrates. The intensities and the frequency of the magnon mode at 18.9cm−1 (M1) showed a discrepancy at the characteristic temperatures of ∼140 and 200K and the magnon mode at 27.9cm−1 (M2) disappeared at ∼200K suggesting spin-reorientation (SR) transition in the epitaxial BFO film. The dc susceptibility measurement showed a large discrepancy near these two temperatures evidently elucidating the spin-reorientation transition mechanism. The partial spectral weight of the magnon modes is believed to be transferred to the lowest phonon mode appearing at 72.8cm−1 and higher magnon mode M2 disappearing near 200K reveal magnon–phonon coupling near to SR transition. [Copyright &y& Elsevier]

Abstract: Li(Ni0.8Co0.1Mn0.1)O2 cathode materials were synthesized by solid-state reaction route. Single-phase layer structure with hexagonal unit cell having symmetry was obtained and the average particle size was around 6μm. Electrochemical studies showed single redox reaction and a maximum charging capacity of ∼140mAhg−1 was obtained. Ex situ structural studies by X-ray diffraction and Raman scattering at various stages of charging and discharging showed that the host layered structure is maintained throughout the electrochemical lithiation–delithiation processes in the 3–4.5V range with systematic change in the lattice parameters. First discharge capacity was 132mAhg−1 and the capacity retention was ∼86% after 20 charge–discharge cycles. [Copyright &y& Elsevier]