First-principles study of the cubic perovskitesBiMO3(M=Al, Ga, In, and Sc)

Abstract

We systematically investigated the structure, electronic properties, zone-center phonon modes, and structure instability of four cubic perovskite BiMO 3 compounds, with three of the M ions being IIIB metals ͑Al, Ga, and In͒ and one IIIA transition-metal Sc, using first-principles density-functional calculations. Optimized lattice parameters, bulk moduli, band structures, densities of states, as well as charge density distributions are calculated and compared with the available theoretical data. Our results are in good agreement with those previously reported in the literature. All the BiMO 3 oxides considered in the present work are semiconductors with an indirect band gap between the occupied O 2p and unoccupied Bi 6p states varying between 0.17 and 1.57 eV. Their electronic properties are determined mainly by Bi-O bonding, which, in turn, depends on the M -O bonding. Ferroelectric properties of these oxides come from the 6s 2 lone pair on the A-site Bi ion and is similarly affected by the M ions through their influence on the Bi-O bonding, as suggested by our calculations of density of state, Born effective charge, and soft modes. The existence of soft modes and eight ͓111͔ minima suggests that the phase transition in BiAlO 3 has a mixed displacive and order-disorder character. There is evidence that ferroelectricity is absent in BiGaO 3 . Our investigation suggests that the BiMO 3 oxides or their modified versions are promising ferroelectric, piezoelectric, multiferroic, and photocatalytic materials.

Observation of Insulating Nanoislands in Ferromagnetic GaMnAs

“…2S 3=2 excitation followed by the absorption of one and two magnons, respectively. These assignments are consistent with the temperature-dependent results and the properties of GaMnAs magnons [16]. First, we note that the measured g is consistent with our interpretation because the magnon g factor is nearly the same as that of Mn 3d electrons [16].…”

“…These assignments are consistent with the temperature-dependent results and the properties of GaMnAs magnons [16]. First, we note that the measured g is consistent with our interpretation because the magnon g factor is nearly the same as that of Mn 3d electrons [16]. Second, the fact that the intensity of peak À1 is significantly smaller at 1.9 K supports our assignment since magnons are thermally excited and, thus, fewer magnons can be emitted at low temperatures.…”

Electronic structure, ferroelectric properties, and phase stability of BiGaO3 under high pressure from first principles

“…The majority of reports is focused on the structural, electronic, and vibrational properties of the pyroxene phase of BiGaO 3 at ambient conditions [5,[11][12][13]. There are also several studies of the perovskite cubic phase of BiGaO 3 [14][15][16][17]. But to our knowledge, there are no theoretical reports concerning pressure-induced structural phase transitions for BiGaO 3 .…”

Peak Effect in the Critical Current of Type II Superconductors with Strong Magnetic Vortex Pinning

“…The OD transition was suggested to be a thermodynamic phase transition induced by thermal fluctuations or pinning centers [2], which has been confirmed experimentally by the direct structural observation of the vortex lattice, such as small angle neutron scattering (SANS) [9], and muon spin relaxation [17]. Also, the investigation of the reversibility of the OD transition provided strong support for its thermodynamical nature [18].However, the exact nature of the PE phenomenon remains controversial [6,7,10,[19][20][21]. Recently, across the PE regime no noticeable change in the order of the vortex lattice was observed by SANS [19], and by Bitter decoration [20].…”

“…Fy, 74.25.Qt One pronounced phenomenon in type-II superconductors is the so called peak effect (PE), which is the appearance of a peak in the critical current density J c before decreasing to 0 with increasing temperature or field [1]. The PE has widely been observed in a variety of low and high temperature superconductors by different experimental techniques [2], such as transport [3][4][5], magnetization [6,7], and ac-susceptibility [8][9][10]. It was proposed long ago that the PE originated from softening of the elastic moduli of vortex lattice [1], which caused by the competitions between elastic energy E el , pinning energy E pin of vortex lattice and the energy of thermal fluctuations E th [11].…”