Visible and ultra-violet emission and absorption spectra of MgAl2O4:Cr

Lou, Feipeng; Ballentyne, D. W. G.

doi:10.1088/0022-3719/1/3/308

Cited by 34 publications

(8 citation statements)

References 5 publications

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“…This observation is not necessarily the case in all spinels. In the normal-spinel series [Mg 2+ ] A [Cr x 3+ ,Al 3+ 2−x ] B O 4 , for instance, it was demonstrated, using optical fluorescence, that the Cr 3+ ion occupies a site of 3m point symmetry, 46 rather than 3m (Table II). Here, the Cr 3+ ion is displaced from a centrosymmetric position to a noncentrosymmetric position, as a consequence of local potential conditions at the octahedral site.…”

Section: Additional Structure Considerationsmentioning

confidence: 99%

Structure of Spinel

Sickafus

Wills

Grimes

1999

Journal of the American Ceramic Society

1,061

590

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This paper reviews the crystal structure of compounds with the general formula AB 2 X 4 , which crystallize with the same atomic structure as the mineral spinel, MgAl 2 O 4 . Three degrees of freedom associated with the detailed atomic arrangements of spinels are considered here: (i) the lattice parameter, a; (ii) the anion parameter, u; and (iii) the cation inversion parameter, i. Oxide spinels are used as examples to explore the interrelationships between these parameters.

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Section: Additional Structure Considerationsmentioning

confidence: 99%

Structure of Spinel

Sickafus

Wills

Grimes

1999

Journal of the American Ceramic Society

1,061

590

View full text Add to dashboard Cite

show abstract

“…A large number of experimental facts, reviewed by Grimes (1971Grimes ( ,1972Grimes ( ,1973, appear to support the proposal of the lower symmetry of certain spinel compositions : off-centre displacements along [ 11 11 of the octahedrally coordinated metal ions (for example Cr3 +) were inferred from x-ray DebyeWaller-factor measurements (Grimes and Hilleard 1970), infrared spectra (Grimes and Collett 1971), electron spin resonance (Stahl-Broda and Low 1959) and optical spectra (Lou and Ballentyne 1968). The optical spectra can only be interpreted by admitting point symmetry 3m for the octahedrally coordinated Cr3+ position; a fact which is incompatible with space group Fd3m, but a strong argument for Fq3m.…”

Section: Introductionmentioning

confidence: 95%

Are antiferroelectricity and other physical properties 'hidden' in spinel compounds?

Schmid

Ascher

1974

J. Phys. C: Solid State Phys.

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Abstract. The piezoelectric switching of antiferroelectric domains by the simultaneous application of an electric field Ei and mechanical stress Tk is proposed as a direct method for examining whether some spinel compositions do have point symmetry 33m and concomitant antiferroelectric ordering as proposed by Grimes.For piezoelectric antiferroelectrics, the switching energy is Ag = 2dij,Ei7;, (d,,, = piezoelectric coefficient). For point symmetry 43m, various possible switching procedures have been described in detail. The smallest coercive product of electric field and stress (E,T,k), is required for switching when the electric field is chosen along cubic [OOl], and directional stress along [llO] or [lTO]. For particular directions, for example [lll], the colinear application of electric field and stress also leads to switching.If the assumed prototype with space group F33m -t h e symmetry proposed by Grimesis supposed to undergo a phase transition leading to ferrimagnetism, the possible symmetries ofthe ferrimagnetic domains are given by the magnetic groups 14m'2', Im'm2 and R3m'. which are M-maximal subgroups of the prototype magnetic group Fz3ml'. All three ferrimagnetic phases permit piezoelectricity, piezomagnetism and the linear and second-order magnetoelectric effect. The tetragonal phase (15m'27 remains antiferroelectric as the prototype is supposed to be, whereas the orthorhombic (Im'm27 and trigonal (R3m') phases become ferroelectric. The full lattice of subgroups of FiT3ml' is presented.

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“…For the spinel materials, however, it has become increasingly difficult to reconcile experimental observations of physical behaviour with the F d 3m sym m etry conventionally assumed by crystallographers. Properties with which difficulties of this kind have arisen include dieletric behaviour (Peters & Standley 1958;Grimes 1973); mag netism (Lotgering 1964;Baltzer et al 1966;Dwight & Menyuk 1967;Grimes & Isaac 1977); heat capacity (Milford & Glasser 1962;Callen 1966;Grimes 1974); infrared spectra (Grimes & Collett 1971;O'Horo et al 1973;Grimes et al 1978); electron spin resonance (Henning & van den Boom 1973) and optical fluorescence spectra (Lou & Ballentyne 1968).…”

Section: Introduction (A) Space Group F D 3mmentioning

confidence: 99%

New symmetry and structure for spinel

1983

Proc. R. Soc. Lond. A

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The crystal structure of magnesium aluminate is conventionally described within a symmetry corresponding to the centrosymmetrical space group Fd3m but this has created difficulties for the interpretation of many of its physical properties. Therefore, extensive X-ray diffraction intensity data have been collected from a small spherical synthetic single crystal and used for a structure parameter refinement assuming F4̅3m symmetry as proposed by Grimes ( Phil. Mag . 26, 1217‒1226 (1972)), and also for refinement according to conventional symmetry. The F4̅3m assumption yields the first direct measurement of the suspected deviations from the centrosymmetrical structure, and is found to provide a significantly superior fit to the experimental data, especially at high angles and with reflexions having structure factors less than 10.0. The weak reflexions include nine that are forbidden under Fd3m symmetry and it is shown that there is satisfactory agreement between observed and calculated structure factors in these cases.

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Visible and ultra-violet emission and absorption spectra of MgAl2O4:Cr

Cited by 34 publications

References 5 publications

Structure of Spinel

Structure of Spinel

Are antiferroelectricity and other physical properties 'hidden' in spinel compounds?

New symmetry and structure for spinel

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