Browsing by Author "Correa, Margarita"

Now showing 1 - 2 of 2
  • Thumbnail Image
    Phase transition and temperature stability of piezoelectric properties in Mn-modified Pb(Mg1/3Nb2/3)O-3-PbZrO3-PbTiO3 ceramics
    Yan, Yongke; Kumar, Amit; Correa, Margarita; Cho, Kyung-Hoon; Katiyar, Ram S.; Priya, Shashank (AIP Publishing, 2012-04-01)
    This study investigates the effect of two different Mn modifiers [MnO2 and Pb(Mn1/3Nb2/3)O-3(PMnN)] on the of phase transitions in Pb(Mg1/3Nb2/3)O-3-PbZrO3-PbTiO3 ceramics. The temperature dependence of polarization derived from measured pyroelectric current indicated change in nature of phase transition with MnO2 doping. This phenomenon was supported by the temperature evolution of the linear softening of low lying hard lattice mode as revealed by Raman analysis. The grain size was found to increase with MnO2 doping (5X) while decrease with PMnN modification (0.5X). Interestingly, the piezoelectric constant of MnO2 modified composition showed negligible degradation (<1%) even after heat treatment very close to the ferroelectric-paraelectric transition temperature. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.3703124]
  • Thumbnail Image
    Phonon anomalies and phonon-spin coupling in oriented PbFe0.5Nb0.5O3 thin films
    Correa, Margarita; Kumar, Amit; Priya, Shashank; Katiyar, Ram S.; Scott, J. F. (American Physical Society, 2011-01-18)
    We present Raman data on both single-crystal and thin-film samples of the multiferroic PbFe0.5Nb0.5O3 (PFN). We show first that the number and selection rules of Raman lines are compatible with a face-centered-cubic Fm-3m structure, as is known in other ABO(3) relaxors, such as PbSc1/2Ta1/2O3. We then compare Raman data with anomalies in magnetization and the dielectric constant near the magnetic-phase-transition temperature (T-N), the diffuse ferroelectric-phase-transition temperature (T-m), and the pseudostructural-phase transition temperature (Burns temperature similar to T-B). The temperature evolution of the Raman spectra for the PFN film shows measurable changes in phonon positions, intensities, and full width at half maxima near 200, 410, and 650 K-temperatures that match well with experimentally observed T-N, T-m, and T-B, respectively. The increase in frequency with increasing temperature for the lowest-energy F-2g phonon mode is particularly unexpected. These changes suggest the transition of the crystal structure from an ordered phase to a disordered phase near T-B. The Raman study revealed phonon anomalies in the vicinity of T-m and T-N that are attributed to the dynamical behavior of polar nanoregions and spin-phonon coupling owing to its relaxor and multiferroic nature, respectively, which is well supported by dielectric and magnetic properties of the PFN thin film. Softening of the Fe-O mode was observed near the T-N. We correlate the anomalous shift of the Fe-O mode frequency with the normalized square of the magnetization sublattice; agreement with the experimental results suggests strong spin-phonon coupling near T-N owing to phonon modulation of the superexchange integral; however, the shifts in frequency with temperature are small (<3 cm(-1)).