Crystal Chemistry, Optical Spectroscopy and Crystal Field Calculations of Co₃TeO₆ and Solid Solutions Co_3–xZn_xTeO₆

Abstract

Solid solutions Co 3-x Zn x TeO 6 (x = 0-3) were prepared both in polycrystalline and single-crystalline form using solid state reactions and chemical vapour transport reactions, respectively. Miscibility between the isotypic end members was established over the complete range (C2/c, Z = 12, a ≈ 14.85, b ≈ 8.83, c ≈ 10.34 Å, ≈ 93°). Crystal structure determinations, performed on basis of single crystal laboratory X-ray (at 295 K) and synchrotron (at 10 and 100 K) data of Co 3 TeO 6 and selected solid solutions, revealed no structural phase transition and allowed a detailed insight into the Co → Zn substitution mechanism. The coordination polyhedra of the five crystallographically independent M 2+ cations are distorted octahedra (for three cations), one distorted tetrahedron and one distorted square [a] Details of all crystal structure investigations can be obtained from Fachinformationszentrum Karlsruhe,

Synthesis and characterization of ternary trielides Na7KTr4 [Tr=In or Tl] including [Tr4]8− Tetrahedra

“…The measure of similarity is 0.006 for Na 7 KIn 4 or 0.003 for Na 7 KTl 4 respectively (see Table 2) and proves that these two structures are highly similar to Na 7 RbTl 4 . Compared to other S‐ or Δ‐values found in the literature [80–82] they are very small indicating a high similarity of these three ternary compounds, which is expected for compounds of the same structure type.…”

CoTeO4 – a wide-bandgap material adopting the dirutile structure type

“…12). Finally, the third and usually most intense 4 T 1g (F) -4 T 1g (P) crystal field transition is located around 18 750 cm À1 within the ascent of the absorption edge, thus slightly reducing its slope up to B20 000 cm À1 ; quite evidently, for 4 T 1g (P) no low-symmetry band splitting could be extracted. The observed approximate crystal field transition energies correspond to a comparatively high crystal field strength parameter of B875 cm À1 , 76 in agreement with the rather small average Co-O distance of 2.087 Å in CoTeO 4 ; the interelectronic repulsion parameter Racah B is B800 cm À1 .…”

“…12) correspond to the first spin-allowed crystal field transition of high-spin Co II in octahedral coordination, i.e. 4 T 1g (F) -4 T 2g (F), split by the distortion of the [CoO 6 ] polyhedron from ideal cubic symmetry, with components located around 7200 (shoulder), 7970, and 9750 cm À1 . The second spin-allowed, but -as two-electron jump in the strong field limit -electronically forbidden and thus weak 4 T 1g (F) -4 A 2g (F) transition, might be spotted roughly around 15 900 cm À1 , within the onset of the absorption edge (see inset in Fig.…”

“…1 For instance, some of these Te-based oxides have interesting physical properties due to their low dielectric losses in the microwave range and show potential applications in the field of low-temperature co-fired ceramic technology. 2 The renewed interest in transition metal oxidotellurates(VI) with formula type A 3 TeO 6 (A is a divalent transition metal) is related to their interesting optical 3,4 and low-temperature magnetic properties, [5][6][7][8] including magnetic field induced spontaneous electric polarization in Co 3 TeO 6 . [9][10][11][12][13][14] Stimulated by these properties, Co 3 TeO 6 has also been investigated in the high-pressure regime.…”

Multianvil high-pressure/high-temperature synthesis and characterization of magnetoelectric HP-Co3TeO6

“…[18][19][20] Due to the good multiferroic properties of Co 3 TeO 6 , this compound has arisen a lot of interest in the last few years and has been well investigated in numerous publications. [18][19][20][21][22][23][24] Lately, we succeeded in the synthesis of a high-pressure polymorph of Co 3 TeO 6 at a pressure of 6.5 GPa and a temperature of 1070 K. It crystallizes in the Ni 3 TeO 6 -type structure. Besides normal-pressure (NP) Co 3 TeO 6 18 and a monoclinic CoTeO 4 , that is related to the rutile structure, 25 HP-Co 3 TeO 6 is now the third existing cobalt tellurate modification.…”