Intermetallic charge-transfer transition in Bi1−xLaxNiO3

Abstract

The nature of triclinic to orthorhombic phase transition, at which colossal negative thermal expansion is observed, and the magnetic ordering of Bi 1−x La x NiO 3 have been investigated with neutron powder diffraction (NPD) and x-ray absorption spectroscopy techniques. The presence of a charge-transfer transition from (Bi/La) 3+ 0.5 Bi 5+ 0.5 Ni 2+ O 3 to (Bi/La) 3+ Ni 3+ O 3 , accompanied by the simultaneous structural distortion, was confirmed. The NPD data also revealed that magnetic ordering is present only in the insulating triclinic phase. The metallic orthorhombic phase was found to be nonmagnetic down to 10 K.

Negative thermal expansion induced by intermetallic charge transfer

“…The strain ΔL / L (400 K) increases with increasing temperature up to 270 K indicating the normal positive thermal expansion, but decreases above 270 K. The average observed α L between 270 and 400 K is −49 × 10 −6 K −1 and the maximum negative slope between 320 and 380 K corresponds to a linear thermal expansion coefficient of −82 × 10 −6 K −1 [24]. It was confirmed that the oxidation of Ni ion from 2+ to 3+ was the origin of this volume shrinkage by XAS measurement [32]. …”

Tuning negative thermal expansion in Bi1−x LnxNiO3 (Ln = La, Nd, Eu, Dy)

“…18,19 Recently, we reported that Bi 0.95 La 0.05 NiO 3 shows a large NTE with a L ¼ À82 ppm/K in the temperature range of 320-380 K, owing to a temperature induced intermetallic charge transfer transition. [20][21][22] The parent compound, BiNiO 3 , has a unique valence state of Bi 3þ 0.5 Bi 5þ 0.5 Ni 2þ O 3 and a triclinic structure, where Bi 3þ and Bi 5þ occupy distinct crystallographic sites. [23][24][25] Substitution of La for Bi stabilizes the valence state of (Bi/La) 3þ Ni 3þ O 3 and leads to temperature-induced melting of charge disproportionation accompanied with simultaneous charge transfer between Bi 5þ and Ni 2þ ions.…”

“…[20][21][22] The XRD patterns were collected at various temperatures with a D8 ADVANCE diffractometer (Bruker) with Cu Ka radiation. The lattice parameters and fractions of low-temperature triclinic and high-temperature orthorhombic phases were refined by conducting a Rietveld analysis using TOPAS software.…”

“…At elevated temperatures, the seven peaks characteristic of the triclinic phase merged into three, indicating there was a structural transition to the GdFeO 3 -type orthorhombic phase; this result is in accordance with our previous report on Bi 1-x La x NiO 3 . 20,22 The structural transition for Bi 0.925 Dy 0.075 NiO 3 was not complete even at 460 K. All samples started decomposing below 500 K. Figure 2(a) shows the temperature dependence of the weighted average volume calculated from the unit cell volumes and the phase fractions refined by Rietveld analysis. NTE with temperature hysteresis was present in all samples.…”

Classical, quantum, and thermodynamics of a lattice model exhibiting structural negative thermal expansion

“…Investigations into the first class of NTE phenomena have revealed contentious issues regarding the interplay of magnetism, disorder, charge disproportionation, and their volume coupling and continue to intrigue physicists [2][3][4][5][6][7][8]. The second class of behavior, which we term structural NTE (SNTE), is observed in both metallic and insulating materials without competing order [9][10][11][12][13][14].…”