Effects of Fe substitution on the electronic, transport, and magnetic properties of ZnGa2O4: A systematic ab initio study

Pisani, L.; Maitra, T.; Valentí, Roser

doi:10.1103/physrevb.73.205204

Cited by 37 publications

(18 citation statements)

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“…These partially filled t 2g orbitals leave the orbital degrees of freedom unfrozen opening up the possibility of orbital order. Moreover, the V-sites in the cubic spinel structure form a pyrochlore lattice, which gives rise to frustrated antiferromagnetic interactions among these sites 9 . In ZnV 2 O 4 the interplay of all these degrees of freedom leads to two successive phase transitions which involve structural, orbital and magnetic changes.…”

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Orbital Order inZnV2O4

2007

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In view of recent controversy regarding the orbital order in the frustrated spinel ZnV2O4 , we analyze the orbital and magnetic groundstate of this system within an ab initio density functional theory approach. While LDA+U calculations in the presence of a cooperative Jahn-Teller distortion stabilize an A-type staggered orbital order, the consideration of relativistic spin-orbit effects unquenches the orbital moment and leads to a uniform orbital order with a net magnetic moment close to the experimental one. Our results show that ab initio calculations are able to resolve the existing discrepancies in previous theories and that it is the spin-orbit coupling alongwith electronic correlations which play a significant role in determining the orbital structure in these materials.PACS numbers: 71.15.Mb, 71.70.Ej Correlated electronic systems involving transition metal oxides took the centrestage of condensed matter physics research for the last three decades because of their intriguing, often non-intuitive properties. Transition metal spinel oxides with an additional complexity of a geometrically frustated lattice provide an exciting ground for the study of several competing interactions among spin, orbital and lattice degrees of freedom 1,2 . Besides being of fundamental interest, spinels have been also proposed for spintronics applications 3,4 . In the present work on ZnV 2 O 4 we investigate the effect of competing spin, orbital and lattice degrees of freedom and show that density functional calculations provide an adequate and realistic ground to establish the dominant mechanism driving the orbital order in vanadium spinels.The orbital order in ZnV 2 O 4 as well as in other vanadium spinels such as MgV 2 O 4 and CdV 2 O 4 is presently a subject of considerable debate 5 . In order to understand the behavior of these compounds, various groups 6,7,8 have proposed alternative microscopic mechanisms which predict different orbital patterns. The ongoing debate has its origin in the complex nature of these systems with competing spin, orbital and lattice degrees of freedom. These systems have V 3+ ions in a spin 1 state characterized by double occupancy of the triply degenerate t 2g (d xy , d xz , d yz ) orbitals. These partially filled t 2g orbitals leave the orbital degrees of freedom unfrozen opening up the possibility of orbital order. Moreover, the V-sites in the cubic spinel structure form a pyrochlore lattice, which gives rise to frustrated antiferromagnetic interactions among these sites 9 . In ZnV 2 O 4 the interplay of all these degrees of freedom leads to two successive phase transitions which involve structural, orbital and magnetic changes. At T S = 51 K, ZnV 2 O 4 undergoes a structural phase transition where the symmetry is lowered from cubic to tetragonal with a compression of the VO 6 octahedron along the c axis 10 and the system possibly orbital orders. The structural transition also lifts the geometrical frustration of the cubic phase making a way for the second transition at T N = 40 K which is ...

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Orbital Order inZnV2O4

2007

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“…Optical properties of several impurity ions in these compounds were studied previously, e.g. Cr 3+ in ZnAl 2 S 4 [2][3][4][5][6][7], Fe in ZnGa 2 O 4 [8]; Mn in ZnGa 2 O 4 [9]; optical properties of ZnGa 2 O 4 nanoparticles were reported in Ref. [10].…”

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confidence: 99%

First-principles calculations of electronic, optical and elastic properties of ZnAl2S4 and ZnGa2O4

Brik

2010

Journal of Physics and Chemistry of Solids

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The optimized crystal structures, band structures, partial and total densities of states (DOS), dielectric functions, refractive indexes and elastic constants for ZnAl 2 S 4 and ZnGa 2 O 4 were calculated using the CASTEP module of Materials Studio package. Pressure effects were modeled by performing these calculations for different values of external hydrostatic pressure up to 50 GPa. Obtained dependencies of the unit cell volume on pressure were fitted by the Murnaghan equation of state, and the relative changes of different chemical bond lengths were approximated by quadratic functions of pressure. Variations of applied pressure were shown to produce considerable re-distribution of the electron densities around ions in both crystals, which is evidenced in different trends for the effective Mulliken charges of the constituting ions and changes of contour plots of the charge densities. The longitudinal and transverse sound velocities and Debye temperatures for both compounds were also estimated using the calculated elastic constants.Key words: A. inorganic compounds; C. Ab initio calculations; D. electronic structure; IntroductionA large group of compounds with spinel structure are generally described by the AB 2 X 4 formula (where A and B are di-and trivalent cations, respectively, and X is a divalent anion). There are two types of cation sites in the spinel structure: tetrahedral for A species and octahedral for B species.Compounds from this family usually have wide band gaps, which can be attractive for various optical applications [1]. Wide band gap also makes these compounds suitable for doping with different impurities to get luminescence in particular spectral region. Optical properties of several impurity ions in these compounds were studied previously, e.g. (X=Al, Ga, In) were calculated from first principles in Ref. [11].In spite of considerable efforts on both experimental and theoretical studies of these compounds, previously reported results for the calculated properties of the bulk materials are somewhat different (comparison between the previous and present calculations will be given below). Besides, it turned out that ab initio calculations of the optical properties and careful studies of the pressure effects on the interionic distances and electron density distribution around ions in these compounds (especially ZnAl 2 S 4 ) are lacking, to the best of the author's knowledge. So, this was one of motivations for the present study, which reports the results of first-principles calculations of a wide range of physical influence of the applied pressure on the charge density distributions, Mulliken charges, and chemical bond orders was considered.The paper is structured as follows: in the next section the crystal structure of the considered crystals and the computational details will be described briefly, then the calculated results will be presented and compared with available experimental data and results of other calculations. The paper will be concluded with a short summary. Crystal str...

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“…The results once again indicate that the formation of Cr clusters leads to quenching of NIRPL in these samples. Both spinels are wide band gap semiconductors and belong to cubic space group Fd3m with lattice parameter a = 8.334 Å for ZnGa 2 O 4 18 (noted as ZGO) and a = 8.2891 Å for MgGa 2 O 4 19 (noted as MGO). Zinc gallate compound crystallizes in normal spinel structure with Zn 2+ ions in tetrahedral coordination and Ga 3+ ions in octahedral coordination with a small cationic inversion.…”

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confidence: 99%

Controlling disorder in the ZnGa₂O₄:Cr³⁺ persistent phosphor by Mg²⁺ substitution

Basavaraju

Priolkar

Bessière

et al. 2017

Phys. Chem. Chem. Phys.

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We have studied in this work the effect of increasing structural disorder on the persistent luminescence of a Cr doped zinc gallate spinel. This disorder was introduced by progressive substitution of Zn by Mg ions, and was studied by photoluminescence, X-ray diffraction, extended X-ray absorption fine structure (EXAFS), X-ray absorption near edge structure (XANES) and electron paramagnetic resonance (EPR) spectroscopy. It was found that increasing the Mg/Zn substitution decreases the number of Cr in undistorted sites and increases the number of Cr with neighbouring antisite defects and with neighbouring Cr ions (referred to as Cr clusters), which in turn decreases the intensity of persistent luminescence. Both XANES and EPR spectra could be simulated by a linear combination of Cr spectra with three types of Cr environments. The increasing disorder was found to be correlated with a decrease of the average Cr-O bond length and a decrease of crystal field strength experienced by Cr ions.

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Effects of Fe substitution on the electronic, transport, and magnetic properties of ZnGa2O4: A systematic ab initio study

Cited by 37 publications

References 29 publications

Orbital Order inZnV2O4

Orbital Order inZnV2O4

First-principles calculations of electronic, optical and elastic properties of ZnAl2S4 and ZnGa2O4

Controlling disorder in the ZnGa₂O₄:Cr³⁺ persistent phosphor by Mg²⁺ substitution

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Effects of Fe substitution on the electronic, transport, and magnetic properties of ZnGa2O4: A systematic ab initio study

Cited by 37 publications

References 29 publications

Orbital Order inZnV2O4

Orbital Order inZnV2O4

First-principles calculations of electronic, optical and elastic properties of ZnAl2S4 and ZnGa2O4

Controlling disorder in the ZnGa2O4:Cr3+ persistent phosphor by Mg2+ substitution

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Controlling disorder in the ZnGa₂O₄:Cr³⁺ persistent phosphor by Mg²⁺ substitution