Comparatively Low Temperature Synthesis, Characterization and Some Physical Studies on Transition Metal Vanadates

2021 ◽  
Vol 13 (2) ◽  
pp. 571-578
Author(s):  
T. Vaz ◽  
A. V. Salker
Keyword(s):  
Transition Metal ◽  
Magnetic Moments ◽  
Band Gap Energy ◽  
Electronic Band ◽  
Photo Degradation ◽  
Triclinic Structure ◽  
Pure Transition ◽  
Co Precipitation ◽  
Electronic Band Structures ◽  
Bonding Characteristics

Pure transition metal vanadates NiV2O6 and CuV2O6 were successfully prepared via co-precipitation technique as low as at 600 °C. The crystal structure and their phase formation were confirmed by X-ray powdered diffraction. Both the compounds were identified to have a single-phase triclinic structure. The bonding characteristics were studied by FTIR spectroscopy. The temperature dependence of electrical resistivity of these vanadates shows a typical semiconducting nature of NiV2O6 and CuV2O6, consistent with their electronic band structures. The calculated band gap energy values of NiV2O6 and CuV2O6 were found to be 2.42 and 2.0 eV respectively, employing a DRS UV-Visible spectrophotometer. Magnetic susceptibility measurements and calculated Magnetic moments confirm their paramagnetic nature. The photocatalytic efficiency was investigated by photo-degradation of methylene blue (MB) solutions employing solar light and found to be promising photocatalysts.

Alkali chalcogenido ortho manganates(II) A6MnQ4 (A=Rb, Cs; Q=S, Se, Te)

2018 ◽  
Vol 73 (11) ◽  
pp. 837-848 ◽  
Author(s):  
Michael Langenmaier ◽  
Tobias Rackl ◽  
Dirk Johrendt ◽  
Caroline Röhr
Keyword(s):  
Magnetic Measurements ◽  
Magnetic Moments ◽  
Electronic Band ◽  
Chiral Structures ◽  
Pure Phase ◽  
Maximum Temperatures ◽  
Alkali Elements ◽  
Electronic Band Structures ◽  
Bonding Characteristics ◽  
Tetrahedral Voids

AbstractThe six isotypic alkali ortho chalcogenido manganates A6[MnIIQ4] (A=Rb, Cs; Q=S, Se, Te) were synthesized – in most cases in pure phase – from stoichiometric mixtures of the manganese monochalcogenides MnQ, the elemental chalcogens and Rb2S/Cs2S2 (sulfido salts) or the pure alkali elements (selenido and tellurido salts) as alkali sources at maximum temperatures between 650 and 800°C. Their hexagonal crystal structures were refined by means of X-ray single crystal data (space group P63mc, Na6ZnO4-type structure, Z=2; A/Q: Rb/S: a=1019.34(2), c=792.560(10) pm, R1=0.0166; Rb/Se: a=1055.74(2), c=821.14(2) pm, R1=0.0275; Rb/Te: a=1126.68(2), c=860.54(2) pm, R1=0.0152; Cs/S: a=1056.68(2), c=831.22(2) pm, R1=0.0168; Cs/Se: a=1096.04(3), c=858.13(2) pm, R1=0.0194; and Cs/Te: a=1167.72(3), c=896.95(2) pm, R1=0.0140). The chiral structures contain isolated C3 symmetric, but very close to ideal tetrahedral, ortho manganate(II) anions [MnIIQ4]6− with Mn–Q distances of 248.7–250.7 (Q=S), 260.7–263.0 (Q=Se) and 280.0–282.4 pm (Q=Te). The chalcogenide ions form a hexagonal closed packing with slightly puckered 36 nets, in which the A(2) cations occupy 3/4 of the octahedral interstices, whereas Mn takes 1/8 and A(1) 3/8 of the tetrahedral voids. Magnetic measurements on the three Cs compounds showed Curie-Weiss behavior down to a temperature of 1.9 K, with magnetic moments significantly reduced with respect to the expected spin-only value of a d5 ion. The electronic band structures of the four salts (Na/Rb)6Mn(S/Te)4, which were calculated within the GGA+U approach, allow a comparison of the chemical bonding characteristics and the magnetic properties within the alkali cation and the chalcogenido ligand series.

Electronic structure and magnetic properties of PbMO3 (M = Fe, Co, Ni) magnetic perovskites: An ab initio study

2014 ◽  
Vol 28 (29) ◽  
pp. 1450205 ◽  
Author(s):  
Aytaç Erkişi ◽  
Erdem Kamil Yıldırım ◽  
Gökhan Gökoğlu
Keyword(s):  
Transition Metal ◽  
Coulomb Interaction ◽  
Transition Metal Oxides ◽  
Density Functional ◽  
Magnetic Transition ◽  
Magnetic Moments ◽  
Local Spin Density Approximation ◽  
Electronic Band ◽  
Half Metallic ◽  
Hubbard U

We present the electronic, magnetic and structural properties of the magnetic transition metal oxides PbMO 3 (M = Fe , Co , Ni ) in cubic perovskite structure. The calculations are based on the density functional theory (DFT) within plane-wave pseudopotential method and local spin density approximation (LSDA) of the exchange-correlation functional. On-site Coulomb interaction is also included in calculations (LSDA+ U ). The systems are considered in ferromagnetic (FM) and G-type antiferromagnetic (G-AFM) order. FM structures are energetically more favored than G-AFM and than non-magnetic states for all the systems studied. The spin-polarized electronic band structures show that all the structures have metallic property in FM order without Hubbard-U interaction (U eff = 0). However, the inclusion of on-site Coulomb interaction (U eff = 7 eV ) opens a semiconducting gap for majority spin channel of PbFeO 3 and of PbNiO 3 resulting in a half-metallic character. PbCoO 3 system remains as metallic with LSDA+ U scheme. Bonding features of all structures are largely determined by the hybridizations between O–p and d-states of transition metal atoms. The partial magnetic moment of Fe atom in PbFeO 3 is enhanced by inclusion of Hubbard-U interaction (2.55 μB ⇒ 3.78 μB). Total magnetic moments of half-metallic PbFeO 3 and of PbNiO 3 compounds are very close to integer values.

THE ELECTRONIC BAND STRUCTURES FOR AN ANTIFERROMAGNETIC STATE OF Cu2Sb-TYPE INTERMETALLIC COMPOUND Cr2As

1993 ◽  
Vol 07 (01n03) ◽  
pp. 770-773 ◽  
Author(s):  
M. SHIRAI ◽  
T. KAWAMOTO ◽  
K. MOTIZUKI
Keyword(s):  
Intermetallic Compound ◽  
Electronic Band Structure ◽  
Magnetic Moments ◽  
Partial Density ◽  
Energy Splitting ◽  
Antiferromagnetic State ◽  
Good Correspondence ◽  
Electronic Band ◽  
Linearized Augmented Plane Wave ◽  
Electronic Band Structures

Electronic band structure calculations are carried out for the antiferromagnetic state of an intermetallic compound Cr2As, having the Cu2Sb-type crystal structure, by using a self-consistent linearized augmented-plane-wave (LAPW) method. The partial density of states (DOS) for Cr (II) 3d states shows a small energy splitting (about 1 eV) between the spin-up and spin-down bands, while that for Cr (I) 3d states hardly shows. The magnetic moments at Cr (I) and Cr (II) sites are evaluated to be 0.33μB and 1.37µB per atom, respectively. These values agree well with the observed values. The calculated DOS shows good correspondence with photoemission and inverse photoemission spectra measured recently.

Electronic Structure of Rare-Earth Pnictides for Metallization of Semiconductors

1994 ◽  
Vol 337 ◽  
Author(s):  
A. G. Petukhov ◽  
W. R. L. Lambrecht ◽  
B. Segall
Keyword(s):  
Experimental Data ◽  
Rare Earth ◽  
Magnetic Moments ◽  
Magnetic Exchange ◽  
Cross Sectional ◽  
Electronic Band ◽  
Lattice Constants ◽  
Rocksalt Structure ◽  
Cohesive Energies ◽  
Electronic Band Structures

ABSTRACTThe results of first-principles calculations of the electronic band structures, equilibrium lattice constants, cohesive energies, bulk moduli, and magnetic moments are presented for the rare-earth pnictides with the rocksalt structure and chemical formula RX, where R = Gd, Er and X = N, P, As. Some of these materials are semimetals and are suitable for metallization of III-V semiconductors. The results for the lattice constants are in good agreement with experimental data. For ErAs, which is closely lattice-matched to GaAs, the calculated magnetic exchange splittings, electron and hole concentrations, Fermi surface cross-sectional areas and cyclotron masses are found to be in satisfactory agreement with the available experimental data.

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