Electrostatically driven charge-ordering in Fe2OBO3

Abstract

letters to nature 658 NATURE | VOL 396 | 17 DECEMBER 1998 | www.nature.com T CO 317 K. Hence a conducting, magnetically ordered state is not found in Fe 2 OBO 3 as T C , T CO . The differences between the estimated activation energies for electron hopping in the chargedisordered (E a < 0 for T . T V ) and ordered (E a < 0:04 eV for T , T V ) 13 states of magnetite and those of Fe 2 OBO 3 (E a < 0:31 eV for E a < 0:35 eV for T . T CO are equal, showing that this small difference is essentially independent of spin alignment, although the ferromagnetic order in magnetite reduces both activation energies by 0.3 eV relative to those in paramagnetic Fe 2 OBO 3 .M

Pressure-induced suppression of charge order and nanosecond valence dynamics in Fe2OBO3

“…Total CO is established over microdomains because of the energy degeneracy of various valence separation configurations. 8,13 Temperature-dependent lattice incommensurate CO has recently been found in the intermediatetemperature range, 280 K < T < 340 K. 8,14 This is also attributed to energy degenerate CO configurations from geometrical frustration effects and the consequent occurrence of thermally activated mobile antiphase boundaries. 8 A valencefluctuating state (melted CO, viz., Fe 2+ ⇔ Fe 3+ electron hopping) ensues at T > 340 K. There is a concomitant structural adjustment from monoclinic→orthorhombic symmetry when this high-temperature valence-fluctuating phase is realized.…”

“…Samples of natural isotopic abundance (2% 57 Fe) used in this work were from the batch of Attfield et al 13,15 in the original discovery of CO in this system. Both x-ray diffraction and 57 Fe ME spectroscopy at ambient pressure confirm that no sample degradation occurred.…”

Comment on “Charge order inFe2OBO3: AnLSDA+Ustudy”

“…They also argued that the a-axis periodicity should be increased by at least a factor two but this a doubling has not been observed. 19,22 They try to justify the absence of insights for CO, hypothesizing that the lack of observation of long-range CO by diffraction is due to the very small CO domains and the superstructure peaks are too weak and broad to be observed. But we disagree with the authors on the fact that the longrange monoclinic lattice distortion was intimately correlated with the occurrence of CO.…”

“…20͒ to carry out a theoretical investigation of the electronic structure of the iron oxoborate ͑Fe 2 OBO 3 ͒. The calculations were made using the P2 1 / c structure of the low temperature phase determined by Attfield et al [21][22][23] First, they conclude a very surprising result using the double ͑2a ϫ b ϫ c͒ supercell, which is that crystallographic equivalent sites Fe͑1͒ and Fe͑2͒ are nonequivalent from the electronic point of view, but Fe͑1͒ and Fe͑2͒ are split into Fe͑1͒ 3+ and Fe͑1͒ 2+ and into Fe͑2͒ 3+ and Fe͑2͒ 2+ , respectively, in view of the authors. We argue to show that this is probably an overstatement.…”

X-ray-induced persistent photoconductivity in vanadium dioxide

“…Metal oxides exhibit diverse ground states and phenomena including high-temperature superconductivity [1], colossal magnetoresistance [2], charge density waves [3], Verwey transitions [4], and metal-insulator transitions (MIT) [5]. Significant attention has been given to the deceptively simple MIT, which has to date been driven with temperature, electric field [6], pressure [7], chemical doping [8], ultrafast laser excitation [9], and ionizing radiation [10].…”