Octahedral oxide glass network in ambient pressure neodymium titanate

Abstract

Rare-earth titanates form very fragile liquids that can be made into glasses with useful optical properties. We investigate the atomic structure of 83TiO2-17Nd2O3 glass using pair distribution function (PDF) analysis of X-ray and neutron diffraction with double isotope substitutions for both Ti and Nd. Six total structure factors are analyzed (5 neutron + 1 X-ray) to obtain complementary sensitivities to O and Ti/Nd scattering, and an empirical potential structure refinement (EPSR) provides a structural model consistent with the experimental measurements. Glass density is estimated as 4.72(13) g cm−3, consistent with direct measurements. The EPSR model indicates nearest neighbor interactions for Ti-O at $$\overline{r}_{TiO}$$ r ¯ TiO = 1.984(11) Å with coordination of $$n_{TiO}$$ n TiO = 5.72(6) and for Nd-O at $$\overline{r}_{NdO}$$ r ¯ NdO = 2.598(22) Å with coordination of $$n_{NdO}$$ n NdO = 7.70(26), in reasonable agreement with neutron first order difference functions for Ti and Nd. The titanate glass network comprises a mixture of distorted Ti-O5 and Ti-O6 polyhedra connected via 71% corner-sharing and 23% edge-sharing. The O-Ti coordination environments include 15% nonbridging O-Ti1, 51% bridging O-Ti2, and 32% tricluster O-Ti3. This structure is highly unusual for oxide glasses melt-quenched at ambient pressure, as it consists of Ti-Ox predominantly in octahedral (with nearly no tetrahedral) coordination.

Microgravity effects on nonequilibrium melt processing of neodymium titanate: thermophysical properties, atomic structure, glass formation and crystallization

“…The second PDF peak is the Nd-O correlation, with r NdO = 2.45 Å and n NdO = 8.4. These values are somewhat different than those from the published structural model 26 : r TiO = 1.984(11) Å and n TiO = 5.72(6); r NdO = 2.598(22) Å and n NdO = 7.70(26). These discrepancies are larger than the typical uncertainty from peak fitting, e.g.…”

“…Density measurements are challenging for fragile liquids and their glasses because melt processing typically requires containerless conditions with small sample volumes. Glass density is typically measured using pycnometry of samples 2–3 mm in diameter, as was done by Arai et al 22 on lanthanum titanate glasses, though this technique can have significant measurement uncertainty for small sample sizes 26 . Melt densities have been measured using backlight imaging techniques in aerodynamic levitation, but partial occlusion of the sample and asphericity introduce an uncertainty of ~5% 33 .…”

“…We recently reported a thorough structural analysis of terrestrial NT glasses 26 , based on X-ray/neutron diffraction and structural modeling, so only brief comments are provided here on the interpretation of the scattering data, focusing specifically on differences between microgravity and terrestrial samples. The glass atomic network has been shown to comprise TiO 5 and TiO 6 polyhedra connected primarily via corner-sharing arrangements, with ~23% edge-sharing, while the Nd 3+ ions act similarly to network modifiers 26 .…”

“…The NT composition is of interest technologically as an optical material: its glass has a high refractive index ( n > 2.1) 21 , 22 and a wide transmission window spanning the visible and infrared range out to ~5 μm 21 , 23 . NT is also of fundamental scientific interest as a fragile liquid 24 and poor glass-former 25 , with an atomic network of octahedrally coordinated Ti-O polyhedra 26 atypical of oxide glasses. Here, we compare the cooling rates, glass formation, and recalescence of molten and supercooled NT processed in the ELF and in a terrestrial aerodynamic levitator.…”

Zinc borate glasses: properties, structure and modelling of the composition-dependence of borate speciation

“…Perhaps, complete vitrification could be accessed up to and including 70 mol% ZnO by employing the levitation melting technique. [45][46][47] For greater than 71 mol% ZnO, chemical separation in the melt is reported. 13 Our investigation supports this finding as a melt containing 73% mol% ZnO was visually observed to be phase-separated, with the bottom layer producing the strong green thermoluminescence characteristic of ZnO.…”