Electrical Properties of Ca-Doped BiFeO₃ Ceramics: From p-Type Semiconduction to Oxide-Ion Conduction

Abstract

The conductivity of Ca-doped BiFeO 3 ceramics varies by many orders of magnitude, depending on the oxygen partial pressure during processing. Bi 1−x Ca x FeO 3−(x/2)+δ ceramics are mixed oxide ion/electron conductors at 800 °C, but the electron conduction can be suppressed; when sintered and cooled in N 2 from 800 °C, they are oxide ion conductors with activation energy ∼0.82−1.04 eV and conductivity ∼1 × 10 −5 S cm −1 at 300 °C, comparable to that of 8 mol % yttria-stabilized zirconia. When heated in O 2 at 125 bar, however, they are mainly p-type semiconductors with conductivity ∼1 × 10 −3 −4 × 10 −5 S cm −1 at room temperature and activation energy ∼0.27−0.40 eV. The oxygen stoichiometry varies over the range 0 < δ < ∼0.016, depending on processing conditions. The semiconductivity is attributed to mixed valence Fe with < ∼3.2% Fe 4+ .

Electrical conductivity and thermopower of (1 − x) BiFeO3– xBi0.5K0.5TiO3(x = 0.1, 0.2) ceramics near the ferroelectric to paraelectric phase transition

“…P-type conductivity is characteristic for the materials in oxidizing atmosphere, while n-type is typical for inert or reducing conditions. A similar p-type behaviour is observed for Ca-substituted, BiFeO 3 , 26 but the minimum in the conductivity as well as the n-type conductivity in bulk BFO-materials has not been reported previously. While the materials were single phase after sintering, it is worth noting that an Fe/Ti-rich secondary phase was observed on the surface of the materials after a long period of electrical DC conductivity measurement (640 and 770 hours for 0.8BFO and 0.9BFO respectively).…”

“…[22][23][24][25][26] The conductivity of 0.7BFO-0.3BKT can be manipulated by thermal treatment in an oxidizing or an inert atmosphere. 20,21 The aliovalent substitution of Fe 3+ with e.g.…”

Direct observation of ferroelectric field effect and vacancy-controlled screening at the BiFeO3/LaxSr1−xMnO3 interface

“…BFO is a good ionic conductor and can readily support oxygen non-stoichiometry. 46,47 Based on the experimental data we argue that oxygen vacancies segregate at the near-surface layer of BFO, but not exactly at the surface, effectively forming a Stern-like double layer. At the same time, the ferroelectric distortion can 10 penetrate into the LSMO region as shown by Tagantsev.…”

Crystallographic and Magnetic Structure of the Perovskite-Type Compound BaFeO2.5: Unrivaled Complexity in Oxygen Vacancy Ordering

“…Perovskite-type compounds have many applications, ranging from electrode materials in solid oxide fuel cells (e. g. La 1-x Sr x CoO 3-d 1 and La 1-x Sr x FeO 3-d 2, 3 ), ferroelectrics (e. g. BaTiO 3 4 ), multiferroics (e. g. BiFeO 3 , Bi 1-x A x FeO 3 -d , A = Ba, Sr, Ca, Pb [5][6][7][8][9][10][11] ) to materials with interesting magnetic properties (e. g. ferromagnetic BaFeO 3 12 (by oxidation of BaFeO 2.5 using O 3 ) as compared with antiferromagnetic BaFeO 2 F compounds [13][14][15] ). The possibility of vacancies on the anion sublattice gives rise to many of the properties of such compounds, including ionic (anionic) conductivity (facilitated by anion vacancies) and electronic conductivity (due to mixed valence) and magnetic order which is often promoted via superexchange interactions via the anions.…”