Na_1/2Bi_1/2VO₃ and K_1/2Bi_1/2VO₃: New Lead-Free Tetragonal Perovskites with Moderate c/a Ratios

Abstract

New lead-free tetragonal perovskites Na 1/2 Bi 1/2 VO 3 and K 1/2 Bi 1/2 VO 3 were synthesized under high pressure (6 GPa) and high temperature (1473 K), based on the design of materials optimizing the lone pair effect of the A-site ion and utilizing the Jahn−Teller effect in the B-site V 4+ . The magnitudes of the c/a ratio and spontaneous polarization, P S , were 1.085 and 108 μC/cm 2 , respectively (73 μC/cm 2 by the point charge model), for Na 1/2 Bi 1/2 VO 3 and 1.054 and 92 μC/cm 2 , respectively (56 μC/ cm 2 by the point charge model), for K 1/2 Bi 1/2 VO 3 , which are comparable to the well-known lead-based ferroelectric PbTiO 3 . This approach can guide the design of new lead-free ferroelectric and piezoelectric materials.

Crystal Structures and Electronic States of High-Pressure-Synthesized (1-x)PbVO3-xBiCrO3 Solid Solutions

“…A clear semiconductive behavior was observed. The activation energy obtained from the Arrhenius plot was E a = 0.28 eV, which is similar to that observed in perovskite-type tetravalent vanadates and trivalent chromates (Mott insulators) [22,24]. The pressure dependence of the electrical resistivity up to 5 GPa was measured because the external field was expected to induce an insulatorto-metal transition or intermetallic charge transfer, as previously observed for PbVO 3 , PbCrO 3 , PbCoO 3 , and BiNiO 3 [2,13,[25][26][27]; results are shown in Figure 7 (b).…”

Negative Thermal Expansion in Lead-Free La-Substituted Bi0.5Na0.5VO3

“…34 Undoped Bi 0.5 Na 0.5 VO 3 exhibited a pressure-induced insulator metal transition around 2 GPa. 25 In this material, the insulatorto-metal transition occurred upon heating at ambient pressure, as a result of the La substitution destabilizing the tetragonal phase.…”

“…Recently, a Bi-based tetragonal perovskite with moderate distortion, Bi 0.5 Na 0.5 VO 3 ( c / a = 1.085 and P s = 73 μC/cm 2 ), has been synthesized . In this material, the effect of the 6s 2 lone pair is weakened, but the tetragonal structure due to the d xy orbital ordering of V 4+ is preserved.…”

A-Site Columnar-Ordered Perovskite CaZnV2O6 as a Pauli-Paramagnetic Metal

“…When the U / W ratio exceeds a critical value, the system exhibits a metal–insulator transition (MIT). MITs in Ca 1– x Sr x VO 3 have been reported in bulk forms with cation substitution or oxygen defects or in thin film forms with a controlled thickness or epitaxial strain. − By contrast, PbVO 3 , A 1/2 Bi 1/2 VO 3 (A = Na or K), and Bi 2 ZnVO 6 are polar insulators with extremely large V 4+ displacements. − The degeneracy of t 2g orbitals is considerably lifted by the first-order Jahn–Teller distortion of V 4+ , leading to an antiferromagnetic insulating state. However, such a colossal V 4+ displacement has only been reported in compounds with stereochemically active A-site cations, namely, Pb 2+ and Bi 3+ .…”