Identification of electronic state in perovskiteCaCrO3by high-pressure studies

Abstract

CaCrO 3 is at the crossover from localized to itinerant electronic behavior, and interpretation of its electronic state has remained controversial. It is a metal from an optical study. However, the collinear type-C antiferromagnetic spin ordering below T N ≈ 90 K is characteristic of localized electron magnetism. We have performed many runs of high-pressure synthesis. CaCrO 3 crystals can be found in some batches. We have used specific-heat measurement as a diagnostic tool to probe the electronic states near the Fermi energy. An electronic bandwidth is broadened by applying high pressure. The magnetization measurement under pressure reveals a dT N /dP < 0.The crystal structural change corresponding to the pressure-induced electron structural change has been monitored by in-situ neutron diffraction under high pressure. The d-electron configuration on octahedral site Cr 4+ is orbitally threefold degenerate. Local site distortions are argued to show that in CaCrO 3 the crossover from localized to itinerant 3d electrons does not result in a charge-density wave in which segregation of the interatomic interactions results in the stabilization of molecular clusters, but in an intraatomic orbital ordering that stabilizes a halffilled localized-electron xy orbital and a ¼-filled c-axis π* band. Local structural changes under pressure reveal a weakening of long-range magnetic order is associated with a smooth MottHubbard transition of the xy electrons.2

Growth and Physical Properties of SrxCa1−xCrO3 Single Crystals

“…The temperature dependence of resistivity measurement results are shown in Figure 10. Although systematic changes with x are not clear, semiconductive behavior was observed for the Sr x Ca 1−x CrO 3 series samples, implying that localized electronic state in this system was consistent with the polycrystalline measurement result and the recent research on its electronic state [10,27,28]. Without the influence of surface pollution and the grain boundary effect, this result should be more accordant with its intrinsic character.…”

“…The sample reported here is close to the nominal composition. Zhou et al [27] measured the specific heat of a single-crystal and polycrystalline CaCrO 3 . The result indicated that the single-crystal sample with oxygen stoichiometry was insulating while the polycrystalline sample with different oxygen content was metallic [27].…”

“…Zhou et al [27] measured the specific heat of a single-crystal and polycrystalline CaCrO 3 . The result indicated that the single-crystal sample with oxygen stoichiometry was insulating while the polycrystalline sample with different oxygen content was metallic [27]. The sample was sensitive to the content of oxygen for its anomalous electronic state, which is located near the localized-itinerant crossover.…”