Short-Range Order and Dynamics in Crystalline α-TeO₂

Abstract

The short-range order and dynamics in crystalline α-TeO2 have been investigated by neutron and X-ray total scattering and by Rietveld refinement of neutron diffraction data. The true lengths of the two bonds in a Te–O–Te bridge are 1.882(1) and 2.117(1) Å, and the high valence, 1.293, of the strong, short bond is balanced by the low valence, 0.686, of the weak, long bond. The root-mean-square (rms) thermal variation, 0.083(1) Å, in the long bond length is nearly twice the rms thermal variation, 0.048(1) Å, in the short bond length because the largest motion of both Te and O atoms is perpendicular to the short bonds. A bond-valence model for the thermal variation in bond lengths, in which both the average and the instantaneous positions of the atoms conform to bond-valence requirements, accounts closely for the observed distribution of Te–O distances in α-TeO2. This has important implications for the interpretation of diffraction experiments on tellurite glasses.

Alkali environments in tellurite glasses

“…The good agreement between the short Te-O bond lengths for Na10 and K10, and for Na19 and K20 reported in Table 2, is evidence that the contribution from in is very small and negligible: In a Te-O-Te bridge, there is a balance between the lengths and valences of the short and long bonds [15]. Thus, if the short bonds in glasses with different alkali are the same length, then the lengths of the long bonds may be expected to also be the same.…”

“…a value taken from Barney et al [15] b value derived from the crystallographic thermal parameters reported by Tagg et al [20] c value estimated in this study; see …”

“…The former are found in pure crystalline -TeO2 [15], while the latter have an arrangement of atoms similar to that present in M2TeO3 crystals [16][17][18]. The change in the local environment of a Te atom from [TeO4E] to [TeO3E] provides an additional NBO in the network, and hence reduces the total number of unfavourable M-BO bonds needed to fulfil the bond requirements of the M + ions [19].…”

Theoretical investigations of the spin Hamiltonian parameters and local tetragonal distortions for Cu2+in crystalline and amorphous TeO2and GeO2

“…Tetragonal α-TeO 2 polymorph was known much earlier than the others [17][18][19][20]. They can be described as different arrangements of corner or edge sharing TeO 4 unit (the distorted trigonal bipyramids) with two longer Te-O bonds (axial bonds) and two shorter ones (equatorial bonds) [21][22][23]. Amorphous TeO 2 has the networks that the basic structural unit is a TeO 4 polyhedron with a lone pair of electrons in one of its equatorial sites and varies with dopants [23,24].…”

“…From the reference distances R (≈ 2.08, 1.89, 1.99 and 1.75 Å for crystalline and amorphous TeO 2 and GeO 2 , respectively [17,22,24,25,[52][53][54][55]) and the self-consistent field functions [56,57], the group overlap integrals S dpt , S dpe , S s and A are calculated and given in Table 1. According to the optical spectral analysis for Cu 2 + in the studied systems and some oxides [14,16], the cubic field parameters Dq and the orbital reduction factors N can be obtained as given in Table 1.…”