High throughput and traditional routes towards functional oxide and oxide-nitride materials

Henderson, Stuart James (2006) High throughput and traditional routes towards functional oxide and oxide-nitride materials. University of Southampton, Doctoral Thesis.

Record type: Thesis (Doctoral)

Abstract

High-throughput methods have been used for the synthesis and preliminary characterisation of optically functional ceramic oxide and oxide-nitride materials on an alumina substrate. Gel routes have been investigated for their viability when used with a Teflon masking system. Three different systems and deposition methodologies have been studied. The first system uses a polymer complex method based on citric acid and ethylene glycol in aqueous media to create arrays of the formula Ca_1-xSr_xZr_1-yCr_yO₃ (0≤ x ≤ 1; 0≤ y ≤ 0.24). Secondly a metal alkoxide sol-gel method using an acetic acid, acetic anhydride solvent has been employed to produce arrays of oxides and oxide-nitrides with the general formulae SrZr_1-xTa_xO₃ and SrZr_1-xTa_xO_2+xN_1-x (0≤ x ≤1). Finally, compounds with the spinel structure in the series Cu_1-xZn_xAl_2-yCr_yO₄ (0≤ x ≤ 1; 0≤ y ≤2) were prepared by co-evaporation. The materials were analysed by rapid sequential X-ray diffraction, scanning electron microscopy and a simple colour measurement technique.

The viability of applying this high throughput methodology to the synthesis and screening of phosphor materials has also been investigated. Arrays of europium doped lanthanum phosphate have been prepared and have revealed that the maximum intensity of the ⁵D₀ → ⁷F₂ red transition is achieved at a composition of (La_0.8Eu_0.2)PO₄. However, increasing the europium content also reduces the ratio of red:orange luminescence, reducing the usefulness of the material as a red phosphor. The compound (Gd_0.75Tb_0.25)P_1.14O_δ was found to be the best green phosphor material from arrays of the type (Gd_1-xTb_x)P_1.14O_δ (0.11≤ x ≤0.27); this replicated previous studies, where the optimum composition, from slightly different conditions, was reported as (Gd_0.83Tb_0.17)P_1.14O_δ.

The structural behaviour of the pyrochlore Bi₂Hf₂O₇ with varying temperature has been studied by powder neutron and X-ray diffraction. The unit cell transforms from monoclinic (a = 15.3536(4) Å, b = 15.3320(4) Å, c = 21.8253(3) Å and β = 90.051(5)°) at room temperature (α-phase) to cubic (a = 21.733(2) Å) at 400°C (β-phase) then to tetragonal (a = 7.68964(3), c = 10.85171(9) Å) at 550°C (γ-phase) and finally to cubic (a = 10.87791(2) Å) at 900°C (δ-phase). The transformations represent a gradual increase in disorder and symmetry with temperature, driven by the need to accommodate the active bismuth lone pair. The four polymorphs characterised are compared to those seen in the related Bi₂Sn₂O₇ system.