A 125Te and 23Na NMR investigation of the structure and crystallisation of sodium tellurite glasses

Alkali environments in tellurite glasses

“…This can be characteristic of a decrease in shielding of the nucleus -i.e. a more ionic environment [13].…”

“…However, in contrast, fits to the main Te-O peak in (fitted over the range 1.68-1.92 Å) for the glasses (Table 2) show significantly less dependence of the mean short Te-O bond length on the alkali cation. It should be noted that Holland et al have reported a metastable crystal phase for Na2Te4O9 that forms first on heating the glass [13]. Although the structure for this crystal phase is unknown, a neutron diffraction study shows that the maximum in the Te-O distribution is at 1.88 Å [51].…”

“…The local structure of alkali M2O-TeO2 glasses (M = Li, Na, and K) has been studied extensively using neutron diffraction [1][2][3][4][5], X-ray diffraction [6,7], EXAFS [7,8], Raman scattering [7,9,10], NMR [2,[11][12][13] and RMC modelling [2,14]. In these studies, particular emphasis was placed on determining the local environment of tellurium and there is a general consensus that the average tellurium coordination number, nTeO, decreases as an oxide modifier is added to the glass network, the change being driven by the bonding requirements of the modifier.…”

125Te NMR chemical shifts and tellurium coordination environments in crystals and glasses in the Ge–As–Sb–Te system

“…However, it is also characterized by a long spin-lattice relaxation time T 1 and displays a large chemical shift range of several thousands of ppm that can make high-resolution 125 Te NMR spectroscopy in the solid state experimentally challenging [4]. Nevertheless, 125 Te solid state NMR spectroscopy has been used extensively for establishment of its chemical shift scale and structural characterization of Te coordination environments in inorganic tellurium salts, MTe (M = Pb, Zn) semiconductors, tellurium oxide based (tellurite) crystals and glasses, transition metal tellurides and organo-metallic compounds [4][5][6][7][8]. However, the chemical shift systematics of 125 Te remain practically unexplored in crystalline and amorphous chalcogenide materials in the Ge-Sb-As-Te system.…”

Mixed network former effects in tellurite glass systems: Structure/property correlations in the system (Na2O)1/3[(2TeO2)x(B2O3)1−x]2/3

“…Large amounts of four-coordinate boron were also detected in zinc borotellurite glasses [17]. Despite considerable experimental effort on different tellurite glasses [18][19][20][21][22] and crystalline model compounds [23] the interpretation of 125 Te NMR chemical shift data in terms of these structures in these glasses is still rather difficult. Wide distributions of isotropic and anisotropic chemical shifts and long spin-lattice relaxation times generally result in rather noisy MAS-NMR spectra with insufficient peak resolution.…”