Abstract: An improvement is proposed in the so-called urea method for the preparation of fine particles of yttrium oxide, according to which, while an aqueous reaction mixture containing a water-soluble yttrium salt, e.g., nitrate, and urea dissolved therein in specified concentrations is heated at 90.degree. to 100.degree. C. to effect precipitation of yttrium carbonate hydroxide particles followed by calcination of the carbonate hydroxide in air into yttrium oxide, the aqueous reaction mixture is diluted with addition of a specified volume of preheated water within a critical period between incipient appearance of turbidity in the reaction mixture by the precipitation of the carbonate hydroxide and a moment 30 minutes thereafter. In this way, the yttrium oxide particles obtained have a globular particle configuration with a very small average particle diameter D.sub.50 in the range from 0.1 to 0.3 .mu.m and are suitable for use in various fine applications.

Abstract: This invention relates to a process for producing metal oxide precipitates, which comprises making a fluoride ion-capturing agent exist in an aqueous solution or hydrofluoric acid solution containing a fluorocomplex compound and/or a fluoride of a rare earth to form precipitates comprising a rare earth oxide or a solid solution containing it as a main component; and a process for producing metal oxide precipitates, which comprises making seed crystal(s) and a fluoride ion-capturing agent exist in an aqueous solution or hydrofluoric acid solution containing a metal fluoro complex compound and/or a metal fluoride of zirconium and/or hafnium to form precipitated crystals comprising said metal oxide crystals or a solid solution containing them as a main component, and is suitable for producing precipitates of a rare earth oxide and crystal precipitates of zirconium oxide and/or hafnium oxide, particularly precipitates such as a thin film, etc.

Abstract: A mixture of an alkali carbonate solvent salt, titanium oxide, an alkaline earth reactant selected from the group consisting of barium oxide, strontium oxide and mixtures thereof, and alkaline earth titanate seed is heated to melt the carbonate salt solvent in which the titanium oxide and alkaline earth reactant dissolve and react precipitating a titanate selected from the group consisting of barium titanate, strontium titanate and mixtures or solutions thereof onto said titanate seed producing large crystal sized powder, said titanate seed not differing significantly in chemical composition from the titanate being precipitated thereon.

Abstract: A process for the manufacture of a polycrystalline garnet containing aluminium and/or gallium and/or indium and at least one element taken from the group comprising the rare earths and yttrium, and to the corresponding monocrystal.

Abstract: A process for the manufacture of a polycrystalline garnet and to the corresponding monocrystal.The process comprises the following steps:(1) a solution containing the salts of the constituent cations of the garnet, in the proportions corresponding to the composition of the latter, is prepared;(2) corresponding hydroxides are co-precipitated by means of a base in order to obtain a co-hydroxide;(3) if appropriate, the co-hydroxide is left to age;(4) it is filtered off;(5) it is washed;(6) it is dried; and(7) it is then calcined at a temperature above the temperature for the formation of the desired garnet structure.The monocrystals obtained by Czochralski drawing of the polycrystalline garnets of the invention can be used, in particular, as substrates in magnetic bubble memory devices.

Abstract: A method for the recrystallization of activated rare-earth oxyhalide phosphors is disclosed. The method comprises recrystallizing the phosphor by firing a phosphor-flux mixture in an inert atmosphere. The phosphor-flux is substantially homogeneous and the flux contains substantially dehydrated magnesium halide. One particularly preferred phosphor made by the method is a lanthanum oxychloride phosphor coactivated with bismuth and ytterbium. This phosphor made by the present method has high speed and low afterglow.

Abstract: Monocrystals based on zirconium or hafnium dioxide stabilized with yttrium oxide having the following proportions of the said elements (in mol. %)Zirconium or hafnium dioxide: 70-90Yttrium oxide: 30-10.Said monocrystals may also contain oxides of the transition or the rare-earth elements or their mixtures in an amount of from 0.01 to 5% of the weight of the monocrystal.The method of producing the monocrystals consists in the preparation of a charge of zirconium or hafnium dioxide and yttrium oxide, melting of the charge, and growing the monocrystals from the obtained melt in the open air by the Stockbarger process.The obtained monocrystals obtained are transparent, colorless, have a high optical quality (a refractive index of n =2-2.2; a transmission band of 2,000-74,000 A), a microhardness of 1,300 to 1,500 kg/mn.sup.2, a dislocation density of 10.sup.3 to 10.sup.5 cm.sup.-2, and with various dimensions (a height of 1 to 8 cm, and a cross section of 0.5 to 4 cm.sup.2).

Abstract: Single crystals of neodymium pentaphosphate greater than one centimeter in size and of high purity and quality are grown from polyphosphoric acid solutions using the combination of a dilute solution, seeding, growth temperatures of 500.degree. to 650.degree. C, and a double crucible configuration.

Abstract: A method of producing the single crystals of the gadolinium molybdate family having a high transmission and low threshold field, comprising the step of growing a single crystal from a melt of the gadolinium molybdate family by a crystal pulling technique, the step of cooling slowly the single crystal in a temperature range of from immediately below a melting point to a segregation temperature of .alpha. phase of the single crystal and the further step of cooling under such cooling conditions that the .alpha. phase is not segregated and the value of the threshold field of the single crystal is not made large in a temperature range of below the segregation temperature of the .alpha. phase.

Abstract: Single crystals, useful as laser emission compounds, having the formula ARF.sub.4 wherein A is potassium, sodium, or lithium, and R is holmium, yttrium, erbium, or dysprosium are prepared by a direct congruent melt crystal growth process that yields crystals exhibiting substantially superior physical and chemical characteristics compared to those grown by conventional methods.

Abstract: Dilithium heptamolybdotetragadolinate, Li.sub.2 Gd.sub.4 (MoO.sub.4).sub.7, is disclosed, along with three methods to prepare it. Two of the three methods are useful for growing single crystals of the material. The material exhibits electro-optic, paramagnetic and ferroelectric properties.