Leakage current and charge carriers in (Na_0.5Bi_0.5)TiO₃thin film

Abstract

A sodium bismuth titanate (Na0.5Bi0.5)TiO3 (NBT) thin film of perovskite structure, synthesized by radio-frequency magnetron sputtering, exhibited a remanent polarization of 11.9 µC cm−2 and a coercive field of 37.9 kV cm−1 at room temperature. It however showed a rather high leakage current density of ∼6 × 10−5 A cm−2 at an applied electric field of 100 kV cm−1. There occurs a change in the controlling mechanism of the electrical behaviours of the NBT thin film from grain interiors to grain boundaries with increasing temperature. The ac conductivity obeys the Jonscher relation. The activation energies for dc conductivity and hopping frequency of the charge carriers are calculated to be 0.92 eV and 1.00 eV, respectively, suggesting oxygen vacancies are the most likely charge carriers at high temperatures. Hopping of oxygen vacancies trapped at the grain boundaries and excitation of polarons in the grain interior are responsible for the relatively high dielectric loss and high dc conductivity. The contribution of hopping charge carriers to the dielectric response is demonstrated by the frequency dispersion observed for the relative permittivity in the low frequency region.

Hopping conduction and low-frequency dielectric relaxation in 5mol% Mn doped (Pb,Sr)TiO3 films

“…The activation energy of oxygen vacancy hopping, very common in the perovskite-type oxides, is reported to be ϳ1 eV. 23,28 This value is far beyond the counterpart in this case. Hence, oxygen vacancy hopping may be ruled out.…”

Dielectric and Pyroelectric Properties of Lead-Free Sodium Bismuth Titanate Thin Films Due to Excess Sodium and Bismuth Addition

“…The ferroelectric behavior of these thin films is inferior to that of bulk ceramics, for which Pr ~30 µC/cm 2 and coercive field Ec~70 kV/cm, which might be associated with the fine grain and low densification of the thin film. 8,14) It is also speculated that these properties of the thin films are affected by slow domain wall motion, which results in the opening of the hysteresis loop at zero field as has been observed for sputtered NBT films. 22) In contrast to NBT ceramics, 23) there are few reports of the pyroelectric properties of NBT thin films.…”

“…So until recently, various processes such as the compositional compensation and/or the ambient control have been widely reported with the aim of preparing pure perovskite NBT films. [6][7][8] In the case of sputtered NBT films, various techniques such as NBT powder bedding process and oxygen atmospheric annealing have been tested. 8,11) In chemically wet processes, excessive Bi addition or excessive Na addition through control of the concentration of Na or Bi source have often been reported.…”

“…[6][7][8] In the case of sputtered NBT films, various techniques such as NBT powder bedding process and oxygen atmospheric annealing have been tested. 8,11) In chemically wet processes, excessive Bi addition or excessive Na addition through control of the concentration of Na or Bi source have often been reported. 6,7,10,12,13) A-site substitution has been employed with other materials with high tolerance factors such as BaTiO 3 and PbTiO 3 to improve their electrical properties by enhancing the purity of the perovskite phase.…”

Influence of annealing on the structure and ferroelectric properties of Sr0.13Na0.37Bi0.50TiO3 thin films prepared by metalorganic solution deposition

“…In recent years, there have been lots of researches focusing on NBT thin films. For example, high quality NBT thin films were prepared by radio-frequency magnetron sputtering, pulsed laser deposition, sol-gel and chemical solution deposition [7][8][9][10][11][12][13][14][15]. The structures and properties of the thin films were also studied.…”