Raman scattering and x-ray diffraction studies of polycrystallineCaCu3Ti4O12under high-pressure

Abstract

We report Raman scattering and x-ray diffraction studies of polycrystalline CaCu 3 Ti 4 O 12 (CCTO) under high pressures. The pressure dependence of several Raman modes was investigated. No anomalies have been observed on the phonon spectra thereby indicating that the T h ͑Im 3͒ structure remains stable up to the maximum pressure ͑5.3 GPa͒ we reached in this experiment. The pressure coefficients for the observed Raman modes were determined. This set of parameters was used for evaluating the stress developed in CCTO thin films. The high-pressure x-ray studies were extended up to 46 GPa and the data confirmed that the T h structure remains stable up to this pressure. The pressure-volume data are well described by the Birch's equation of state. The experimental value of the zero pressure bulk modulus is B 0 = 212± 2 GPa. Grüneisen parameters of CCTO were also determined.

Towards materials with enhanced electro-mechanical response: CaCu3Ti4O12–polydimethylsiloxane composites

“…CCTO is predicted to have eight symmetry modes but usually only five of them are observed, classified as TiO 6 rotation-like modes: A g (1) (444 cm À1 ), F g (2) (453 cm À1 ) and A g (2) (510 cm À1 ), and Ti-OTi stretching modes of the octahedron: F g (3) (576 cm À1 ) and F g (4) (710 cm À1 ), assigned as asymmetric and symmetric modes, respectively. 31 In the ceramic CCTO powder only three bands are detected, corresponding to the A g (1), A g (2) and F g (3) modes. Raman spectra of PDMS and CCTO-PDMS composite are presented in Fig.…”

Dielectric Properties of Ca0.7Bi0.3Ti0.7Cr0.3O3 (CBTC)–CaCu3Ti4O12 (CCTO) Composite

“…The band at 576 cm À1 is assigned to the Ti-O-Ti anti-stretching mode of the TiO 6 octahedra. 17 The F g (4) mode has been predicted to be observed at about 710 cm À1 . The mode 761 cm À1 is assigned to the symmetric stretching breathing of the TiO 6 octahedra.…”

“…In a previous work, Valim and co-workers 17 elucidated that CCTO has a body-center cubic primitive cell that contains 20 atoms and belongs to the centrosymmetric T h (Im3) group. The standard group theory analysis predicts that the Raman active modes are distributed among the irreducible representation as 2A g + 2E g + 4F g. 18 CCTO is a weak scatter and only five of the eight predicted modes are observed at around 444 cm À1 , 453 cm À1 , 510 cm À1 , 576 cm À1 , and 761 cm À1 , as shown in Fig.…”

“…3. Based on lattice dynamics studies 19,20 and polarized Raman measurements, 17 the mode symmetries are identified as A g (1)(444 cm À1 ), F g (2)(453 cm À1 ), A g (2)(510 cm À1 ), F g (3)(576 cm À1 ), and F g (4)(761 cm À1 ). Following lattice dynamics calculations, 444 cm À1 , 453 cm À1 , and 510 cm À1 are TiO 6 rotation-like modes.…”

“…Its low intensity is typical of the structures containing shared units in which the neighboring octahedral damps the symmetric vibrations. 17 CBTC 1-Àx -CCTO x composites were compacted in pellets and measured the dielectric properties, such as K and D, as shown in Figs. 4 and 5, respectively.…”