Abstract
Partial replacement of Ti4+ by Te4+ ions in calcium copper titanate lattice improved its dielectric behaviour mostly due to cubic-to-tetragonal structural transformation and associated distortion in TiO6 octahedra. The relative permittivity values (23–30 x 103) of Te4+ doped ceramics is more than thrice that of un-doped ceramics (8 x 103) at 1 kHz. A decreasing trend in relative permittivity with increasing temperature (50–300 K) is observed for all the samples. Barrett’s formula, as a signature of incipient ferroelectricity, is invoked to rationalize the relative permittivity variation as a function of temperature. A systematic investigation supported by temperature dependent Raman studies reveal a possible ferroelectric transition in Te4+ doped ceramic samples below 120 K. The possible ferroelectric transition is attributed to the interactions between quasi-local vibrations associated with the micro-clusters comprising TiO6 and TeO6 structural units and indirect dipole-dipole interactions of off-center B–cations (Ti4+ and Te4+) in double perovskite lattice.
Highlights
Thin-films and hetero-structures based on perovskite oxide ferroelectrics have been the subject of extensive study as these are of potential importance for a wide variety of device applications that include non-volatile ferroelectric memories, dynamic random access memories, tunable microwave devices etc.[1,2,3] Recently, there is an increasing interest on CaTiO3 or SrTiO3 type materials, which are known to be incipient ferroelectrics,[4,5] owing to their tremendous potential for device applications
We present here the results pertaining to the temperature dependent dielectric and Raman spectroscopic studies carried out on undoped and doped CCTO ceramics that revealed the presence of modes associated with tetragonal (I4/mmm) crystal structure and give ample evidence for the presence of incipient ferroelectricity besides the structural transformation occurring in this compound at a low temperature
The mid-frequency regime, i.e., 104 to 5x105 Hz, dielectric constant values of around 16000 for CCTTO2, 12000 for CCTTO1 and 7000 for CCTO are attributed to the permittivity response of insulating grain boundaries (GB) in the ceramic samples
Summary
Thin-films and hetero-structures based on perovskite oxide ferroelectrics have been the subject of extensive study as these are of potential importance for a wide variety of device applications that include non-volatile ferroelectric memories, dynamic random access memories, tunable microwave devices etc.[1,2,3] Recently, there is an increasing interest on CaTiO3 or SrTiO3 type materials, which are known to be incipient ferroelectrics,[4,5] owing to their tremendous potential for device applications. There was a recent report on ACu3Ti4O12 family with Na+ and Bi3+ occupying A site, i.e., Na0.5Bi0.5Cu3Ti4O12 (NBCTO) which is iso-structural with CCTO with Im3 cubic symmetry and is known to be an incipient ferroelectric.[14] The infrared and terahertz spectroscopic data of NBCTO revealed the splitting and softening of low frequency modes (34, 71, 100, 124 and 136 cm-1) corresponding to the mixed occupancy of Na+ and Bi3+ ions on the A site This made us more inquisitive especially to visualize the effect of partially replacing B-site (Ti4+) by Te4+ (5s2 lone pair) in ACu3Ti4O12 class of double perovskites on their structures and physical properties. We present here the results pertaining to the temperature dependent dielectric and Raman spectroscopic studies carried out on undoped and doped CCTO ceramics that revealed the presence of modes associated with tetragonal (I4/mmm) crystal structure and give ample evidence for the presence of incipient ferroelectricity besides the structural transformation occurring in this compound at a low temperature
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