Melting of d_xy Orbital Ordering Accompanied by Suppression of Giant Tetragonal Distortion and Insulator-to-Metal Transition in Cr-Substituted PbVO₃

Abstract

PbVO 3 features giant tetragonal distortion (c/a = 1.23) and spontaneous polarization (P s = 101 μC/cm 2 ) originating from the ordering of d xy orbital of V 4+ with single d electrons. A dedicated study of Cr-substituted PbVO 3 prepared by high-pressure synthesis afforded a well-defined variation in c/a ratio. Ensuing changes in atomic structure were correlated to ferroelastic domain switching and a temperature-induced structural transition to a cubic phase accompanied with an insulator-to-metal transition and a negative thermal expansion.

Intermetallic Charge Transfer in V-Substituted PbCrO3

“…The cubic structure same as that of PbCrO 3 was observed for x ≤ 0.60. In the heavily V substitution side ( x > 0.60), the splittings of the (100) c and (110) c peaks indicating the tetragonal ( P 4 mm ) structure were observed as previously reported . We have reported the ferroelastic property and NTE for 0.75 ≤ x ≤ 0.85 as well .…”

“…The slight increase in the volume for 0.4 ≤ x ≤ 0.6 should be attributed to the larger ionic radius of V 4+ (0.58Å) than that of Cr 4+ (0.5Å). Further V substitution results in the 12% volume expansion owing to the transition to the polar tetragonal PbVO 3 -type structure as previously reported Figure shows the Pb-4f HAXPES spectra for x = 0, 0.35, and 0.40.…”

Emergence of a Cubic Phase Stabilized by Intermetallic Charge Transfer in (1 – x)PbVO3–xBiCoO3 Solid Solutions

“…Note that PbVO 3 and BiCoO 3 are Mott insulators. GT perovskites have been regarded as promising candidates for colossal NTE materials. − Their huge c / a ratio and P S induce a colossal NTE accompanied by the ferroelectric-to-paraelectric phase transition. Our recent studies have reported that electron-doped PbVO 3 , that is, Pb 1– x Bi x VO 3 ( x = 0.20 and 0.30) and Pb 0.76 La 0.04 Bi 0.20 VO 3 , exhibited a colossal NTE that reached a volume shrinkage of ∼8% and is one of the largest NTE materials reported so far .…”

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

“…The phase transition was not completed at temperatures up to 700 K. The fraction of the cubic phase decreased with decreasing temperature; however, approximately 16% of the cubic phase remained even at 100 K, as shown in Figure 9. The tetragonal-to-cubic phase transition may be accompanied by an insulator-to-metal transition, as in the case of Cr-substituted PbVO 3 [14]. The presence of trivalent chromium ions weakens the Jahn-Teller effect and may introduce electronic itinerancy, which may trigger phase transition in 7/8PbVO 3 -1/8BiCrO 3 .…”

“…First, an intermetallic charge transfer and a complex valence state can be expected because of the close energy of the valence orbitals of chromium, vanadium, and lead ions. Second, an insulator-to-metal transition similar to that of PbV 1-x Cr x O 3 may occur [14]. Herein, the evolution of the crystal structure, valence state, and electronic properties of (1 − x)PbVO 3 − xBiCrO 3 (x = 1/8 − 7/8) solid solutions were studied.…”