B.M. Wanklyn

Flux growth of some complex oxide materials

This paper describes the preparation of the following complex oxide crystals which have not previously been grown by the flux method: FeNbO4, MnWO4, CoWO4, NiWO4, RMn2O5 (R = Er to Sm, and Y), RMnO3 (R = Er to Gd), LaOCl, La2Ti2O71, Bi2Sn2O7, and PbTiP2O8. Single crystal X-ray diffraction data are reported for the latter material, the preparation of which has not previously been reported, and for La2Ti2O7 and Bi2Sn2O71, for which only powder data were previously available. Improved methods for the growth of Mn3O4, LaCoO3, RPO4 (R = Yb to Gd), RCrO3 (R = Lu, Yb), ErOF and NaNbO3 are also reported.

Crystal growth from the flux systems PbOV2O5 and Bi2O3V2O5

Abstract Fluxes of composition 2PbO·V 2 O 5 and 4Bi 2 O 3 ·V 2 O 5 have been found to be particularly suitable for crystal growth. Starting compositions and conditions for growth are given for Al 2 O 3 , Cr 2 O 3 , α -??? 2 O 3 , β -Ga 2 O 3 , ThO 2 , TiO 2 , GaFeO 3 , NiFe 2 O 4 , NiTiO 3 , Fe 2 TiO 5 , TbNbO 4 , ThPbV 2 O 8 and RVO 4 (R = rare earth ion).

The flux growth of single crystals of rare earth perovskites (orthoferrites, orthochromites and aluminates)

Abstract Rare earth orthoferrite crystals RFeO 3 (R = La to Yb and Y), up to 1 cm edge, were grown by slow cooling in PbO-PbF 2 -B 2 O 3 flux. The isothermal evaporation method was used to grow the rare earth orthochromites RCrO 3 (R = La to Yb) and lanthanum aluminate crystals doped with more than 0.1% Cr 3+ ; in all cases 5 mm edge crystals were obtained. The rare earth aluminates (R = Gd, Tb, Dy) were prepared as transparent untwinned crystals several mm. on edge. Different fluxes and growth techniques were required for each of these.

Flux growth of rare earth vanadates and phosphates

Optically clear crystals of rare earth vanadates and phosphates have been grown from Pb/sub 2/V/sub 2/Cl and Pb/sub 2/P/sub 2/Cl respectively by slow cooling. Experimental techniques for the recovery of both crystals and fluxes by hot-pouring are described. The temperatures of the antiferromagnetic transitions and Jahn- Teller distortions shown by the crystals are tabulated. (auth)

Microhardness of flux grown pure doped and mixed rare earth aluminates and orthochromites

The results of microhardness measurements on flux-grown crystals of (i) single (pure) rare earth aluminates RAlO3 (R = Eu, Gd, Dy, Er) and rare earth orthochromites RCrO3 (R = Y, Gd, Yb), (ii) rare earth aluminates doped with neodymium, erbium, ytterbium and holmium, and (iii) mixed rare earth aluminate crystals of the type (La1−x) Pr(x)AlO3 (x=0, 0.25, 0.75 and 1.00) are presented. The variations in the microhardness value with load are non-linear in all cases. Kicks law fails to explain the observed variations. Instead, they are best explained by the application of the idea of materials resistance pressure in the modified law proposed by Hays and Kendall. The results indicate that the doping does not increase the hardness value of crystals in all cases. The hardness instead depends on the composition of the parent material as well as the dopant entering into the crystal lattice. Mixed rare earth aluminate crystals are shown to be harder than those of single rare earth aluminates.

The prediction of starting compositions for the flux growth of complex oxide crystals

Abstract The flux growth of complex oxides from systems which contain a refractory oxide, an acidic or amphoteric oxide, and a basic oxide (or oxide + fluoride) is considered. It is shown that the growth of a desired compound may require an excess of the acidic or amphoteric oxide to be included in the melt, and that this is related to the difference between the melting points of the refractory oxide and the acidic or amphoteric oxide. When the melting-point differences are large, melts with a relatively high concentration of basic oxide/fluoride have produced crystals larger and more nearly equidimensional than those obtained when relatively less basic oxide was present. A correlation is demonstrated between an increase in the number of bond-breaking anions provided by the basic oxide/fluoride component and the growth of more nearly equidimensional crystals. A generalised pseudoternary composition diagram is provided as a model in determining starting compositions likely to produce the desired binary or ternary oxide. This model has been successfully applied to the flux growth of the zircon family compounds (ZrSiO 4 , ThSiO 4 , ZrGeO 4 , ThGeO 4 ), compounds in the system Dy 2 O 3 -K 2 O-MoO 3 (Dy 6 MoO 12 , Dy 2 MoO 6 and DyKMo 2 O 8 ), and to PrBO 3 , DyVO 4 , DyPO 4 , Co 2 SiO 4 and other materials. It is suggested that a good flux for oxides is one which contains the greatest proportion of discrete tetrahedral or triangular complex anions compatible with crystallisation of the desired phase.

Effects of modifying starting compositions for flux growth

Abstract The effects of modifying starting compositions for the flux growth of some compounds, each containing a refractory and an acidic oxide, have been investigated. It has previously been proposed on the basis of limited evidence that fewer, larger and more nearly equidimensional crystals are formed (a) when the excess of the acidic oxide component necessary for the formation of the compound in the flux is reduced to a minimum (b) when part of the basic oxide component is replaced by the corresponding fluoride (c) when the acidic oxide component is partly replaced by other acidic oxides. Evidence for these proposals is now extended to include RPO 4 (R = rare-earth), RVO 4 , R 2 Ge 2 O 7 , RKMo 2 O 8 , RBO 3 , R 2 GeMoO 8 , ZrSiO 4 , ThGeO 4 , and Er 2 Si 2 O 7 , and new starting compositions for producing crystals of these materials are given.

Microhardness measurements on single crystals of flux-grown rare earth perovskites (orthoferrites, orthochromites and aluminates)

The results of indentation-induced microhardness testing studies of flux-grown single crystals of rare earth orthoferrites, RFeO3 (R=Gd to Er and Yb), rare earth orthochromites RCrO3 (R=La, Eu and Dy), and rare earth aluminates RAlO3 (R=La, Sm, Gd, Eu and Ho) are presented. The variation in the value of microhardness with load is observed to be non-linear in the case of all these materials. It is found that the results are not in accordance with Kicks law. The results have been analysed and the applicability of the idea of materials resistance pressure in the modified law as proposed by Hays and Kendall [Metallography6 (1973) 275] is discussed.

The growth of ZnO crystals from phosphate and vanadate fluxes

Abstract ZnO crystals have been grown from compositions corresponding to 2.84 ZnO · V 2 O 5 , 4.1 ZnO · P 2 O 5 , and 3.2 ZnO · (P, V) 2 O 5 by slow cooling from 1300 °C to 900 °C. Transparent crystal plates 2 cm across, 0.3 mm in thickness, with resistivity similar to that of vapour grown ZnO, were obtained.

Phase diagram and single crystal growth of (La, Sr)2CuO4 from CuO solution

The system (La,Sr)2CuO4-CuO has been investigated by differential thermal analysis (DTA), thermogravimetric analysis (TGA) and slow-cooling flux growth experiments. The phase diagram is given and was used in the crystal growth experiments. The crystal products have been characterised by EPMA and by X-ray powder pattern and single crystal techniques. Large single crystals have been grown from CuO as flux by spontaneous nucleation and top seeding.