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A new oxide CaCr_(0.5)Fe_(0.5)O_3 was prepared under high pressure and temperature conditions. It crystallizes in a B-site disordered Pbnm perovskite structure. The charge combination is determined to be Cr~(5+)/Fe~(3+) with the presence of unusual Cr~(5+) state in octahedral coordination, although Cr~(4+) and Fe~(4+) occur in the related perovskites CaCrO_3 and CaFeO_3.The randomly distributed Cr~(5+) and Fe~(3+) spins lead to short-range ferromagnetic coupling, whereas an antiferromagnetic phase transition takes place near 50 K due to the Fe~(3+)–O–Fe~(3+) interaction. In spite of the B-site Cr~(5+)/Fe~(3+) disorder,the compound exhibits electrical insulating behavior. First-principles calculations further demonstrate the formation of CaCr_(0.5)~(5+)Fe_(0.5)~(3+)O_3 charge combination, and the electron correlation effect of Fe~(3+) plays an important role for the insulting ground state. CaCr_(0.5)Fe_(0.5)O_3 provides the first Cr~(5+) perovskite system with octahedral coordination, opening a new avenue to explore novel transition-metal oxides with exotic charge states. 相似文献
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We study the effect of strain on band structure and valley-dependent transport properties of graphene heterojunctions. It is found that valley-dependent separation of electrons can be achieved by utilizing strain and on-site energies. In the presence of strain, the values of transmission can be effectively adjusted by changing the strengths of the strain, while the transport angle basically keeps unchanged. When an extra on-site energy is simultaneously applied to the central scattering region, not only are the electrons of valleys K and K' separated into two distinct transmission lobes in opposite transverse directions, but the transport angles of two valleys can be significantly changed. Therefore, one can realize an effective modulation of valley-dependent transport by changing the strength and stretch angle of the strain and on-site energies, which can be exploited for graphene-based valleytronics devices. 相似文献
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The spin current in a parabolically confined semiconductor
heterojunction quantum wire with Dresselhaus spin--orbit coupling is
theoretically studied by using the perturbation method. The formulae
of the elements for linear and angular spin current densities are
derived by using the recent definition for spin current based on spin
continuity equation. It is found that the spin current in this
Dresselhaus spin--orbit coupling quantum wire is antisymmetrical,
which is different from that in Rashba model due to the difference in
symmetry between these two models. Some numerical examples for the
result are also demonstrated and discussed. 相似文献
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Banach空间中广义集值变分包含问题的迭代解 总被引:1,自引:0,他引:1
本文研究Banach空间中一类广义集值变分包含问题 ,建立了广义集值变分包含问题的迭代解的一些算法 ,并统一和推广了一些最新文献中的结果 . 相似文献
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