Raman Responses in Mechanically Activated BaTiO₃

Abstract

The structure and lattice dynamics of mechanically activated BaTiO 3 was investigated in this study. Phonon behavior and crystal structure stability of the obtained nanocrystalline BaTiO 3 were discussed from the view point of crystallite size effects and microstrains induced by mechanical activation. A systematic study of Raman responses indicates that mechanical activation has a distinct influence on BaTiO 3 lattice spectra affecting the intensity, width, and position of Raman modes. The measured Raman spectra were deconvoluted and phonon parameters were estimated. It has been established that applied mechanical activation leads to a significant decrease in the mean crystallites size, but nevertheless enables formation of tetragonal nanocrystalline BaTiO 3 .M. Hoffman-contributing editor Manuscript No. 31363.

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“…The patterns show diffraction peaks that correspond to tetragonal BaTiO 3 of P4mm space group (JCPDS # 01-075-1606). 14,22 All the patterns present a secondary phase corresponding to BaCO 3 , in agreement with literature. 14,25 One possible source of this phase comes from the high surface reactivity of BaTiO 3 nanoparticles with dissolved CO 2 resulting in carbonate formation.…”

“…14,22 All the patterns present a secondary phase corresponding to BaCO 3 , in agreement with literature. 14,25 One possible source of this phase comes from the high surface reactivity of BaTiO 3 nanoparticles with dissolved CO 2 resulting in carbonate formation. Due to high basicity of BaO, which constitutes 50% of the vicinal (100) surfaces, BaCO 3 is formed on the surface of the nanoparticles through the formation of CO 3 2À from dissolved CO 2 species during synthesis.…”

“…These peaks corresponds to those reported for the tetragonal phase of BaTiO 3 . 14,35,36 These spectra further conrm that the tetragonal phase remains the dominant phase in all samples. The acquired Raman spectra are deconvoluted into a series of Lorentzian-shaped peaks (Fig.…”

“…While the second order peaks at 270 cm À1 and 518 cm À1 persist in the cubic phase, the Raman peaks located at 310 cm À1 and 715 cm À1 are rst order modes of the room temperature tetragonal BaTiO 3 phase. 13,14,35,37,38 In particular, the 310 cm À1 Raman mode represents the torsional vibration of Ti-O 3 when the TiO 6 octahedron undergoes an order-disorder transition. 39 By comparison of the spectra of the different samples, we observe a signicant drop in intensity of 306 cm À1 and 713 cm À1 Raman peaks as the Cr 3+ content increases.…”

“…BaTiO 3 is known to exist in different structural phases as a function of temperature, size and dopants. The high-temperature paraelectric phase shows no spontaneous electric polarization due to Ti-atom occupying the centrosymmetric sites with respect to oxygen 13 while the orthorhombic (Amm2, <0-5 C), rhombohedral (R3m, <À80 C), tetragonal (P4mm, <120 C) 14,15 and high temperature hexagonal (P4/mmm, 1460 C) phases 16 exhibit a ferroelectric response. Ferroelectrics, being non-centrosymmetric, present the bulk photovoltaic effect (BVPE), which signicantly contributes to enhanced photoactivity.…”