Structural evolution of bismuth sodium titanate induced by a-site non-stoichiometry: Neutron powder diffraction studies

Abstract

We performed neutron powder diffraction measurements on (Bi0.5Na0.5+x)TiO3 and (Bi0.5+yNa0.5)TiO3 to study structural evolution induced by the non-stoichiometry. Despite the non-stoichiometry, the local structure (r ≤ 3.5Å) from the pair distribution function analysis is barely affected by the sodium deficit of up to -5 mol%. With increasing pair distance, however, the atomic pair correlations weaken due to the disorder caused by the sodium deficiency. Although the sodium and the bismuth share the same crystallographic site, their non-stoichiometry have rather opposite effects as revealed from a distinctive distortion of the Bragg peaks. In addition, Rietveld refinement demonstrates that the octahedral tilting is continually suppressed by the sodium deficit of up to -5 mol%. This is contrary to the effect of the bismuth deficiency, which enhances the octahedral tilting.

Bismuth Sodium Titanate Based Materials for Piezoelectric Actuators

“…Small compositional deviations of either A-site cations or Ti cation have been shown to influence the crystal structure, ceramic microstructure and piezoelectric properties [51,54,95,96,97,98,99,100,101]. Either Na deficiency or Bi excess in the nominal starting composition enhances the dc resistivity, d 33 but lowers T d , octahedral tilt angle and ceramic grain size [54,96,97,98].…”

“…Either Na deficiency or Bi excess in the nominal starting composition enhances the dc resistivity, d 33 but lowers T d , octahedral tilt angle and ceramic grain size [54,96,97,98]. On the other hand, either Na excess or Bi deficiency lowers the RT dc resistivity, d 33 but enhances T d , octahedral tilt angle and ceramic grain size [54,96,97,98]. Figure 4 shows the variations of d 33 , T d , relative permittivity and loss tangent with Na and Bi stoichiometry.…”

“…Small compositional deviations of either A-site cations or Ti cation have been shown to influence the crystal structure, ceramic microstructure and piezoelectric properties [ 51 , 54 , 95 , 96 , 97 , 98 , 99 , 100 , 101 ]. Either Na deficiency or Bi excess in the nominal starting composition enhances the dc resistivity, d 33 but lowers T d , octahedral tilt angle and ceramic grain size [ 54 , 96 , 97 , 98 ]. On the other hand, either Na excess or Bi deficiency lowers the RT dc resistivity, d 33 but enhances T d , octahedral tilt angle and ceramic grain size [ 54 , 96 , 97 , 98 ].…”

Influence Of Fabrication Condition on the Microstructural and Optical Properties of Lead-Free Ferroelectric Bi\(_{0.5}\)Na\(_{0.5}\)TiO\(_{3}\) Materials

“…The sol-gel method is an effective and low cost method for synthesis of ceramics. However, the loss of Na element during synthesis affects dramatically on stoichiometry of synthesized BNT ceramics and subsequently it will impact strongly on the ferroelectric and optical properties, as well as photocatalytic activity [8,9]. In this aspect, A-site nonstoichiometry that could occur at any step of the process will cause intrinsic defects [8].…”

Piezoelectric Ceramics of the (1 − x)Bi0.50Na0.50TiO3–xBa0.90Ca0.10TiO3 Lead-Free Solid Solution: Chemical Shift of the Morphotropic Phase Boundary, a Case Study for x = 0.06

“…The T and R phases coexist over a rather broad interval of temperatures [9]. In addition to this structural complexity, non-stoichiometry affects both structure [10] and properties [11]. At sintering temperatures ( T s > 1000 °C) Bi 2 O 3 and Na 2 O are volatiles, which result in changes in the stoichiometry.…”