SiO2, ZrO2, B2O3 and MgO oxides and their combinations were used as sintering aids for preparation of yttrium aluminum garnet (YAG) ceramics doped by Nd2O3, Er2O3, Ho2O3, Tm2O3 and Yb2O3. The influence of these additives on optimal sintering temperature, grain growth, volume of residual pores and optical quality of the ceramics were investigated. The best combination of the sintering additives was found and high quality samples of YAG:Nd (1 at.%) ceramics were obtained. The original method of laser optical quality characterization of ceramics was developed and tested. The main laser parameters of YAG:Nd (1 at.%) ceramics samples are measured and compared with the best well known laser ceramics. The samples of YAG:RE (RE- Er2O3, Ho2O3, Tm2O3 and Yb2O3) ceramics are obtained, and their optical transmittance spectra are measured. Composite structures of YAG:Yb (5 at.%) - YAG were obtained by the simplest method of successive joint compaction of different composition layers.

The effect of sintering aids of SiO2, ZrO2, B2O3, and MgO oxides on the optimum sintering temperature, ceramics grain growth, total volume of residual pores, and optical quality of obtained ceramics is studied. The best combinations of sintering aids are found; as a result, YAG:Nd (1 at%) samples of ceramics of high optical quality are obtained. An original method for characterizing laser properties of ceramics is developed. Comparative measurements of main laser characteristics of the obtained ceramics and ceramics of the Konoshima Chemical Corp. Ltd wellknown in the world practice, are performed.

Чистые и легированные ионами Nd и Yb керамики иттрий-алюминиевого граната и (Y,La)2O3 лазерного качества с оптическим пропусканием в области лазерной генерации около 1 мкм более 80% получены методом твердофазного синтеза с использованием неагломерированных нанопорошков Y2O3 и Al2O3. Нанопорошки Y2O3 получены методом лазерного испарения и химического осаждения в растворах мочевины, а также путем помола промышленного Y2O3 в специально сконструированном лабораторном аттриторе со скоростью вращения мешалки до 1500 об./мин. Для синтеза керамики ИАГ был использован промышленный Al2O3. Все нанопорошки после помола имели размер частиц порядка сотни нанометров. Спекание в вакуумной печи при 1615–1750°C компактов, полученных из этих нанопорошков, дало высокопрозрачные образцы керамики.

Undoped and Nd- or Yb-doped laser-grade yttrium aluminum garnet and (Y,La)2O3 ceramics with a transmittance above 80% in the 1-μm lasing region have been prepared by solid-state reactions using nonagglomerated Y2O3 and Al2O3 nanopowders. The Y2O3 nanopowders were prepared via laser evaporation, chemical precipitation from urea solutions, and grinding of commercially available Y2O3 in a purposedesigned laboratory-scale attritor at stirrer rotation rates of up to 1500 rpm. The YAG ceramics were prepared using commercially available Al2O3. After grinding, all of the powders had a particle size on the order of a hundred nanometers. Green compacts produced from the nanopowders were sintered in a vacuum furnace between 1615 and 1750°C to give highly transparent ceramic samples.

We have considered the problems of agglomeration of yttrium aluminium garnet (YAG) nanopowders prepared by chemical co-precipitation of precursors from aqueous solutions and subsequent calcination. To fabricate YAG and Y2O3 laser ceramic samples with high optical transmittance and reproducible characteristics, we have developed a method for producing non-agglomerated nanopowders of pure and doped Y2O3 by homogeneous chemical precipitation. Nanopowders Y2O3 with La and Yb as well as mixtures of Y2O3: Nd and several commercial nanopowders of aluminium oxide have been compacted; optimised compacting technique have been selected; ceramic samples (Y, La, Yb)(2)O-3 and YAG: Nd with high optical transmittance at a wavelength of 1 mu m have been produced by solid-phase synthesis.

Y3Al5O12(YAG) laser ceramics can be produced now as large size samples with excellent quality. We studied YAG ceramics doped with d(1) Ti3+ and Zr3+ ions as possible broad-band materials for tunable and ultra-short pulses lasers. The procedure of doped YAG ceramics fabrication included chemical co-precipitation, precursors' heat treatment, YAG powder grinding, high pressure colloidal slip-casting for nanopowders compaction and vacuum sintering of performs at 1730-1800 degrees C. Transparent colored samples were obtained. Absorption and luminescence spectra of ceramics samples are similar to the spectra of correspondingly doped YAG single crystals. Zr3+ luminescence excited by second harmonic of Nd:YAG laser was observed for the first time. Possibility to obtain laser action is discussed.

Method of preparation YAG laser ceramics using nanopowders obtained by calcining of precursors deposited from nitrate solutions with ammonium bicarbonate as a precipitant was developed. Rheological properties of slurries with different deflocculant concentrations were investigated. High-pressure colloidal slip-casting (HPCSC) method was used for nanopowders compactions, and preforms with green density up to 60% were obtained. Application of HPCSC compaction method reduces the requirements to starting nanopowders. Transparent YAG ceramics were obtained by sintering of compacts at 1700–1800°C in vacuum. Laser action was achieved in plate ceramics samples with longitudinal pumping by semiconductor laser. Possibilities of improvement of laser output parameters are discussed.

We developed a new method for fabrication of oxide laser ceramics. Its prospects were conclusively confirmed by efficient lasing at two wavelengths approximate to 1064 nm (F-4(3/2) -> I-4(11/2)) and approximate to 946 nm (F-4(3/2) -> I-4(9/2)) of Nd3+ ions in Y3Al5O12 ceramics with laser-diode pumping. (c) 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Nanopowders of Nd-doped yttrium oxide were obtained by chemical co-precipitation method using nitrate salts solutions and different precipitant agents - urea, ammonium carbonate and oxalic acid. Precursor and oxide particles agglomeration, particle form, particle size and specific surface area depend critically upon experimental conditions. Plates and rods were formed with hydroxycarbonate and oxalates precipitation correspondingly, whereas hydroxynitrates gave more uniform spherical particles’ shapes. Calcination at 900–1200°C gave oxide powders with specific area in the range 15–50m2/g. High energy ball milling was used to decrease grain agglomeration. Powders with around 100nm size were used to prepare pellets by slip casting into porous moulds using PMMA or PAA additives to reduce viscosity of the slurries with high powder contents. The pellets density around 0.48–0.52 of the theoretical value was obtained. Vacuum sintering of the pellets at 1700–1800°C gave transparent ceramic samples with grain size between 10 and 50μm. The most serious defects in the ceramics are closed pores which reduce their transparency.

The coagulation of particles from water-heterogeneous systems in the field of a confocal ultrasonic resonator is studied. It is found that, at frequencies of several megahertz, when acoustic power of about 1 W is applied to the resonator, long stable filaments consisting of the material of the heterogeneous system are formed in the vicinity of the resonator axis. The filaments consist of thin disks formed by coalescent particles spaced at intervals strictly equal to half of the sound wavelength. The features of this coagulation are determined for suspensions of various nature (metal and dielectric particles, colloidal solutions, and oil emulsions). It is established that the coagulation in a standing acoustic wave occurs faster than under natural conditions (under the influence of gravity). The possibility of using this effect for cleaning liquids from impurities and separating hyperfine particles without employing filter materials is discussed.

A new principle of designing a SAW gas sensor is described. This sensor, being essentially of sorption type, also offers properties of thermometric SAW sensors. The basic idea here is that heat fluxes propagate between the SAW substrate and the working surface of the temperature-regulating system with some delay. A sensor based on this principle can detect not only the vapors of volatile substances but also gases by their thermal properties, retaining high temperature stability and speed of response unlike conventional SAW thermometric sensors. The design of this sensor built around a LiNbO 3 SAW delay line is described, and experiments on detecting a household propane-butane mixture with this sensor are reported. In particular, the responses of the sensor are measured at different gas-flow rates, two different SAW substrate temperatures, and two propane-butane concentrations. Ways of improving the sensor’s performance are discussed.

The basic principles of a new surface acoustic wave (SAW) gas sensor are described. Being essentially a sensor of the mass-sensitive type, the proposed device possesses certain features of the thermometric SAW sensors and is not only sensitive to the vapors of volatile substances, but capable of detecting gases by their thermal properties as well. This principles consists of making a certain delay of heat fluxes between the substrate of sensitive SAW element (SAW delay line or SAW resonator) and working surface of the sensor's temperature stabilization system. In contrast to the known thermometric SAW sensors, the proposed sensor is characterized by high temperature stability and fast response. A variant of the sensor based on a LiNbO/sub 3/ is described and some results on detecting propane-butane mixtures are presented, glass spacers being a means providing heat flux delay between LiNbO/sub 3/ substrate and working surface of the sensor's temperature stabilization system.

A tunable gas sensor using surface acoustic waves (SAW) is described. It is designed on the basis of a waveguide delay line fabricated on a piezoelectric substrate made of 128° Y-cut LiNbO 3 . A voltage applied between the waveguide and two electrodes causes a local change in the properties of the substrate near the waveguide and differently affects the sensor’s response to the vapors of various analytes. Some results of the experimental study of the sensor, which show the change in the selectivity under the effect of voltage, are presented. The analytes used for testing include a number of alcohols and deionized water. The possibilities for employing such a sensor in the sensor arrays of gas analyzers of the electronic nose type are discussed.

A new configuration of surface acoustic wave (SAW) gas sensors based on SAW waveguide devices with relatively narrow aperture of several wavelengths is suggested. This suggested configuration permits to impart to SAW sensor a new feature such as a certain electronic tuning of chemical selectivity (without sensitive coating) by applying electric voltage between this waveguide and two planar electrodes closely placed on the substrate aside the waveguide. Furthermore due to rather narrow aperture it permits to improve sensor's important characteristic such as threshold mass detectability. Sensors with this narrow waveguide configuration, by our opinion, are promising for application in modern gas analysis systems like electronic nose (E-nose) and portative chromatograph applications

A new tunable SAW chemical sensor suitable for applications in sensor arrays is proposed and demonstrated experimentally. The sensor is based on a SAW delay line with a metallic waveguide on the surface of the piezoelectric substrate. An electrical voltage applied between this waveguide and two electrodes placed on the substrate surface next to the waveguide gives rise to local perturbations of the substrate properties in the vicinity of the waveguide, thus leading to a variation in the sensor selectivity for different chemical vapours. The device was used to sense several types of alcohol vapours; experimental results are presented.

The influence of radiation in the visible spectral range on the growth rate and composition of ZnSxSe1−x during the usual metal-organic chemical vapour deposition process was observed. This fact was used to grow the superlattice under pulse radiation from a xenon or tungsten lamp directed at a GaAs substrate. Superlattices with periods of 60–1500 Å were obtained by this method.