Search

In this article, we report the structural phase transitions in Bi4 V2 O11 as observed from temperature-dependent Raman scattering and X-ray diffraction measurements. Four different types of highly disordered coordination polyhedra around the vanadium atoms with large dispersion of V-O bond lengths are observed in Bi4 V2 O11 at ambient temperature. The observed V-O bond lengths could be grouped into two categories, viz. shorter <1.7 Å and longer >1.7 Å. The Raman modes of Bi4 V2 O11 could be assigned to vibration of these bonds and V-O-V linkages. We could correlate the difference in degree of anharmonicity of the phonon modes with temperature to differences in V-O bond strength. The local structure of vanadium-oxygen network in Bi4 V1.8 Cu0.2 O10.7 was also obtained by similar studies. The effect of highly disordered anion sublattice in the doped compound is reflected in the broadening of the Raman modes. [ABSTRACT FROM AUTHOR]

The present work reports detailed structural and electrical studies on A-site substituted La x Gd 1-x InO 3 (0.0 ≤x ≤ 1.0) system with structurally different end members in search for tailored lead-free relaxors. The motivation is the possibility to manipulate the crystal structure to maneuver electrical properties in hexagonal GdInO 3 , a candidate for geometric ferroelectricity. The hybrid synthesis protocol involving gel-combustion led to stabilisation of metastable polymorphs in some nominal compositions due to kinetic stabilisation. Non-preference of La3+ for 7- fold coordinated A-site in hexagonal structure manifested in wide-ranging orthorhombic phase field prevailing even in Gd3+-rich region, also supported by theoretical studies. P-E studies on Gd3+-rich compositions exhibited hysteresis loop which suddenly became narrow for the nominal composition La 0.4 Gd 0.6 InO 3 with very low remanent polarisation. This along with broad maximum exhibited in plot of dielectric constant vs temperature that shifts to higher T upon increasing frequency, for La 0.4 Gd 0.6 InO 3 , supports presence of relaxor-type behavior. Signature of hexagonal-type vibrations in otherwise bulk orthorhombic (by XRD) La 0.4 Gd 0.6 InO 3 and anomalous trend in La/Gd vibrational mode along with narrowing down of Raman modes have been cited as plausible structural reasons for the relaxor behaviour. This has significance in context of structure-electrical property relationship leading to development of potential lead-free relaxors. [Display omitted] • Detailed phase evolution in GdInO 3 (P6 3 cm)- LaInO 3 (Pnma) with composition and T. • C-type metastable phases observed by synthesis route endowed kinetic stabilisation. • Non-preference of La3+ for 7-fold capped octahedra yields wide orthorhombic field. • Extremely low field independent leakage current (4 × 10−5 μA/mm2) observed for GdInO 3. • New lead-free relaxor by A-site distortion by 40 mol%La3+ substitution in h-GdInO 3. [ABSTRACT FROM AUTHOR]

Structural and functional applications involving La 2 Zr 2 O 7 exploit the data on fluorite to pyrochlore phase transition, because of the strong dependence on the physical properties of the system with its phase stability. Though studied for decades, the origin of fluorite to pyrochlore phase transition in La 2 Zr 2 O 7 is still not well understood. In this article, we confirm the presence of a fluorite to pyrochlore phase transition in La 2 Zr 2 O 7 system in the temperature range 1000–1450 °C. The phase transition along with the associated structural properties is investigated with the help La 2 Zr 2 O 7 samples calcined at different temperatures. [ABSTRACT FROM AUTHOR]

Abstract: The formation of strained layers and a non-monotonic evolution of strain in high energy (100MeV) silver ion (Ag7+) irradiated undoped semi-insulating GaAs are observed and analyzed using Raman scattering and high resolution X-ray diffraction (HRXRD) measurements. At low fluence, compressively strained layers are formed, whereas, with increase in fluence both compressive and tensile strains appear as observed from HRXRD measurements. Further, at low fluence, the change in compressive strain with increase in fluence is found to be sharper than what is observed at higher fluence, thereby suggesting a critical fluence value, beyond which there is a simultaneous generation and annihilation of vacancy type defects. The initial blue shift and subsequent relative red shift beyond above critical fluence in the Raman peak also qualitatively reveal non-monotonic evolution of strain in this case. Finally, we demonstrate the sensitivity of Raman spectroscopy in detecting the decrease in lattice ordering in the crystal in the low fluence regime, below the detection limit of Rutherford back-scattering channeling (c-RBS) measurements. [Copyright &y& Elsevier]