Effect of the Reoxidation on Positive Temperature Coefficient Behavior of BaTiO₃–Bi_0.5Na_0.5TiO₃

Abstract

As a positive temperature coefficient of resistivity (PTCR) material, (1−x)BaTiO3–x(Bi0.5Na0.5)TiO3 (BT–BNT, 0.01≤x≤0.08) ceramics without any donor doping were prepared by a conventional solid‐state reaction method. All samples were sintered in an N2 atmosphere at 1340°C, followed by reoxidizing at 800°–1100°C in air. The PTCR characteristics of BT–BNT ceramics were investigated in terms of BNT content, reoxidation temperature, and time. Room‐temperature resistivity (ρRT) of simples sintered in N2 decreased to 102Ω·cm, and the jump in resistivity (maximum resistivity [ρmax]/minimum resistivity [ρmin]) was enhanced by three orders of magnitude through a suitable reoxidation process without sacrificing the ρRT. The Curie temperature (Tc) was shifted to a high temperature (>130°C) with an increase in the BNT content. With the addition of 4 mol% BNT, the obtained ceramic exhibited a low ρRT of 2 × 102Ω·cm, a typical PTC effect of ρmax/ρmin>103, and a Tc of 160°C.

Enhanced insulating and piezoelectric properties of BiFeO3‐BaTiO3‐Bi0.5Na0.5TiO3 ceramics with high Curie temperature

“…A reduced leakage current density with a minimum value of ~ 10 −8 A/cm 2 was obtained at x = 0.05 after adding NBT. The reduced leakage current density could be due to the redundant Na + , which acts as acceptors and increases the insulating property . Similar phenomena were observed in BNT‐doped BT ceramic and Na‐doped BF ceramic .…”

“…The volatilization of Bi 3+ is more serious than Na + since the melting point of Bi 2 O 3 (ca 820°C) is much lower than that of Na 2 O (ca 1275°C). The redundant Na + tended to distribute at the grain boundaries and inhibit the grain growth . As increasing x , the inhibiting effect increases, and is predominant at x = 0.07, leading to refined grain.…”

“…The grown grain is attributed to the increased Bi 25 FeO 40 which would form liquid phase and benefit the grain growth in sintering . The decreased grain size is caused by the redundant Na + at the grain boundaries, which would inhibit the grain growth . BNT was unstable and could decompose into Bi 2 O 3 and Na 2 O during the sintering .…”

“…BNT ceramic is a representative perovskite ferroelectric material with excellent ferroelectric property ( P r = 38 μC/cm 2 ) and high T C of 320°C . It was found that the resistivity of BT can be significantly increased by two orders of magnitude after adding BNT . It is reasonable to infer that the resistivity of BF‐BT ceramics can be increased by the addition of BNT to form a ternary solid solution, which would benefit the poling and piezoelectric property.…”

“…On the other hand, adding the third number (SrZrO 3 , Bi(Zn 0.5 Ti 0.5 )O 3 , Bi(Mg 1/2 Ti 1/2 )O 3 and so on) into BF and ion substitution for Fe 3+ and/or Bi 3+ by Sc 3+ , Sm 3+ or Dy 3+ have been tried to enhance the insulating property in BF‐BT ceramics . But there were few reports that relate to the addition of the third number into BT to enhance the insulating property in BF‐BT ceramics. BNT ceramic is a representative perovskite ferroelectric material with excellent ferroelectric property ( P r = 38 μC/cm 2 ) and high T C of 320°C .…”