The effects of defect system ordering in a weakly doped incipient ferroelectric (KTaO₃): dielectric manifestation

Abstract

The temperature-frequency behaviour of the permimivily d(T, f) and m[S(T. f)] (20-300 K, 120 Hz-9 MHz), EPR, optical absorption and luminescence of KTaO3, nominally pure and weakly doped (0.1 ~1 % Li: 0.01 wt% Cr; 3 wt% Cu; I wi% Fe; 0.1 wt% Li+O.l wt% CI and 0.1 wt% L i t 0 . l wt% Crt0.02 wt% Cu) were studied. Below 70 K, in all doped samples, dielecuic dispersion CCCUIS, with m[S(T)l maxima positions obeying rhc universal Arhenius law with activation energy A = 1000 * 50 K. This is associared with local ordering in the dipoledipole Clusters containing reorienting defect pairs of various kinds, with correlations due to interaction via t h e m soft mode.

Free charge localization and effective dielectric permittivity in oxides

“…A step towards understanding the physical origin of these losses was taken when Bidault et al 39 could successfully show that such losses are by no way restricted to KTaO 3 single crystals since they were observed in more than 50 perovskite samples of different composition, morphology and ferroelectric properties (standard ferroelectrics, quantum paraelectric and quantum ferroelectrics). Even more interesting was the common activation energy of about 100 meV which was found in all these compounds and later confirmed in additional materials 41 and fitted previous data. 42 Such a common trend is shown in Fig.…”

“…Whatever their composition, growth type, morphology and ferroelectric properties of the samples fall on this same Arrhenius line. 39,41,42 Only pure and Ca substituted SrTiO 3 does escape from this common trend with a much lower temperature range for the dielectric losses and a bending down pointing at zero energy activation at ultralow temperatures. 39,[45][46][47] The linear extrapolation at higher temperatures of this dielectric relaxation fit well the higher frequencies ESR 50 and Brillouin scattering data in SrTiO 3 .…”

Incipient ferroelectric to a possible ferroelectric transition in Te4+ doped calcium copper titanate (CaCu3Ti4O12) ceramics at low temperature as evidenced by Raman and dielectric spectroscopy

“…Though our group reported various physical properties of this material, the specific report concerning the incipient ferroelectric characteristics of CCTO prompted us to take up the investigations that are reported over here. [10][11][12] It was demonstrated that the permittivity (ε r ) value associated with the bulk response (10-120 K) decreases with increasing temperature for both single crystals (10-55 K) and ceramics (60-110 K) of CCTO which is consistent with incipient ferroelectricity obeying the Curie-Weiss law with a negative Curie temperature. This result facilitated establishing the structureproperty correlations similar to that of many other titanate-based perovskites associated with B-site octahedral tilting.…”

“…9 According to the reports in the literature, insertion of small amounts of dopants at A or B-site of these incipient ferroelectrics has a profound effect on their dielectric and structural properties, viz, triggers relaxor or ferroelectric behaviour. 10,11 In cubic double perovskite AA 3 B 4 O 12 family, a dubious compound calcium copper titanate (CaCu 3 Ti 4 O 12 , CCTO) drew the attention of many researchers around the globe. 12 There exists ample literature on structural and physical properties (especially dielectric) of this compound with no undisputed conclusions.…”

Paramagnetic dipole centers inKTaO3:Electron-spin-resonance and dielectric spectroscopy study

“…4,9,10,24,and 25͒. Peak of dielectric losses at TӍ40 k was observed in almost all KTaO 3 samples, whose intensity being sample dependent. In particular, the level of crystal purity defines intensity of the peak and it becomes almost unobservable (tan ␦Ͻ10 Ϫ4 ) in the samples fabricated from the highest purity component or carefully cleaned from the unavoidable impurities.…”