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Low‐Temperature Dielectric Relaxations Associated with Mixed‐Valent Structure in Na 0.5 Bi 0.5 Cu 3 Ti 4 O 12
Author(s) -
Sun Xiaohong,
Wang Chunchang,
Wang Guojing,
Lei Changmei,
Li Teng,
Liu Lina
Publication year - 2013
Publication title -
journal of the american ceramic society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.9
H-Index - 196
eISSN - 1551-2916
pISSN - 0002-7820
DOI - 10.1111/jace.12208
Subject(s) - dielectric , analytical chemistry (journal) , materials science , polaron , relaxation (psychology) , bismuth , activation energy , dielectric loss , atmospheric temperature range , chemistry , metallurgy , thermodynamics , psychology , social psychology , physics , optoelectronics , chromatography , quantum mechanics , electron
We, herein, present comparative investigations on the Na 0.5 Bi 0.5 Cu 3 Ti 4 O 12 ceramic samples with and without 10 mol% excess of Na / Bi . The samples were prepared by the standard solid‐state reaction technique. The dielectric properties of the sample were investigated in the temperature (93–320 K) and frequency (20 Hz–10 MHz) windows. Three thermally activated dielectric relaxations observed in Na 0.5 Bi 0.5 Cu 3 Ti 4 O 12 with the activation energies of 0.104, 0.267, and 0.365 eV for the low‐, middle‐, and high‐temperature dielectric relaxations, respectively. Only the low‐temperature relaxation was observed in both Na and Bi excessive samples. X‐ray photoemission spectroscopy results revealed the mixed‐valent structures of Cu + / Cu 2+ and Ti 3+ / Ti 4+ in Na 0.5 Bi 0.5 Cu 3 Ti 4 O 12 sample, but only Ti 3+ / Ti 4+ in Na and Bi excessive samples. Our results showed that the dielectric properties of the investigated samples are strongly linked with these mixed‐valent structures. The high‐ and low‐temperature relaxations were attributed to be a polaron‐type relaxation due to localized carriers hopping between Cu + / Cu 2+ and Ti 3+ / Ti 4+ , respectively. The middle‐temperature relaxation is suggested to be a dipole‐type relaxation caused by the defect complex of bismuth and oxygen vacancies.