Double phase conjugation in copper-doped potassium sodium strontium barium niobate crystals

We show a double phase conjugator with novel crystals of copper-doped potassium sodium strontium barium niobate. The phase conjugation reflectivity can reach 278% and depends on relative input positions of both incident beams. The response time with the input beam power ratio is measured and modeled as a function of input beam power ratio. The formation of the arch coupling loop is analyzed with theoretical simulation results and a positive feedback process is proposed. The influence of a self-pumped phase conjugation process on double phase conjugation fidelity is also discussed. It is necessary to avoid generating self-pumped phase conjugation to prevent the reduction of double phase conjugation fidelity.     

常压烧结制备透明铌酸钾钠陶瓷

在铌酸钾钠(KNN)陶瓷中掺杂锂和铋的氧化物作为晶粒生长抑制剂,用常压烧结工艺制备了铌酸钾钠透明陶瓷(K0.48-0.5xNa0.52-0.5xLixNb1-xBixO3,x=0.04～0.15)材料。研究了掺杂量、烧结工艺条件对陶瓷透明性、光电系数、晶相结构和微观形貌的影响。当x=0.09时,厚度为0.5mm陶瓷样品的红外透光率达到82%,光电系数为6.06×1011m/V。     

Optical phase singularities in detection of laser beam collimation

Optical phase singularities, also called optical vortices, are known to have applications in various branches of optics. Here the role played by optical vortices in collimation testing is explained. Interference and a diffractive experimental setup in which the presence of an optical vortex permits collimation testing are presented. It is shown that the moire fringes that aid in collimation detection are due solely to the presence of vortices and not to the accompanying phase factors that are involved in producing a grating structure.     

碳纳米管复合铌酸钠钾压电陶瓷的制备和研究

采用传统固相反应法制备了铌酸钠钾(KNN)粉体,在该粉体中添加碳纳米管(CNT)后,制备成CNT-KNN复合材料,研究了该复合材料的介电和压电性能。实验发现CNT的添加没有改变KNN压电陶瓷的晶体结构。少量的CNT添加(0.02‰(质量分数))提高了压电性能,过多的CNT(0.02‰(质量分数))会导致压电性能降低。同时发现,CNT的添加降低了样品的介电常数,介电性能明显依赖于密度关系。     

A new phase transition in sodium niobate

The temperature dependences of the dielectric constant ε of sodium niobate single crystals NaNbO₃ and sodium niobate-based (Na,Li)NbO₃ and (Na,K)NbO₃ solid solutions with low content of the second component have been studied. A weak anomaly observed in ε(T) indicates a new phase transition in the vicinity of 150°C in NaNbO₃. The introduction of lithium or potassium into NaNbO₃ crystals increases the temperature of this transition. The X-ray powder diffraction data suggest that the new transition takes place between two rhombohedral phases.     

Growth and characterisation of ferroelectric potassium lithium niobate crystals

Abstract

Potassium lithium niobate crystals have been grown by the resistance heating Czochralski technique. The optical transmission spectrum of the crystal has been determined. The results showed that the spectrum properties of potassium lithium niobate crystals grown from a melt with a higher Li₂O content are better than that of crystals grown from the melt with a lower Li₂O content. The crystals grown by this method have good quality and second harmonic generation properties. Frequency doubling results of a quasi cw-Ti:sapphire laser using crystal samples showed that potassium lithium niobate can be used to double the frequency of near infrared quasi cw-lasers in the 890–960 nm wavelength range.     

Synthesis and processing of nanosized sodium potassium niobate powders

Abstract

Sodium potassium niobate powders have been produced successfully using a Pechini sol–gel method modified with a novel niobium precursor. The decomposition of the gels produced by this method was observed with thermogravimetric analysis and evolved gas mass spectrometry. This showed three main weight loss stages up to 1000°C arising from the loss of water, methane and carbon dioxide. The effect of different heat treatments of the equimolar gel was studied and correlated to particle properties and phase development. The resultant calcined powders were nanosized and single phase with some residual organic material and water. The effect of varying the composition between sodium niobate and potassium niobate was also studied and correlated to particle size and phase development.     

Optical detection of the anesthetic agent propofol in the gas phase

The anesthetic agent propofol (2,6-diisopropylphenol) is the most widely used intravenously administered drug in general anesthesia. However, a viable online capability to monitor metabolized levels of propofol in patients does not currently exist. Here we show for the first time that optical spectroscopy has good potential to detect metabolized propofol from patients' exhaled breath. We present quantitative absorption measurements of gas phase propofol both in the ultraviolet and middle-infrared spectral regions. We demonstrate that a detection limit in the subparts-per-billion concentration range can be reached with photoacoustic spectroscopy in the UV spectral region, paving the way for the development of future optical monitors.     

Nonequilibrium phase transitions

A brief review is provided of the subject of nonequilibrium phase transitions occurring in various systems in different disciplines. All these systems exhibit a similar kind of ordering phenomena at a macroscopic level and can therefore be classified in terms of appropriate order parameters. Typical order parameter equations are discussed in the light of Landau’s phenomenological theory of phase transitions. The instabilities occurring in a few chemical reactions are discussed in some detail and the role of fluctuations pointed out. Mention is also made of the possibility of viewing some metallurgical phenomena as examples of nonequilibrium phase transitions.     

Conductivity in allotropic phase transitions

A method is given for calculating the resistivity as a function of temperature in the presence of structural phase transitions in solids.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 37, No. 2, pp. 329–335, August, 1979.     

Preparation of potassium tantalate niobate through sol–gel processing

Potassium tantalate niobate (KTN) KTa_0.65Nb_0.35O₃ powders and thin films of perovskite structure were prepared through sol–gel processing. A homogeneous and stable precursor solution was obtained from tantalum ethoxide, niobium ethoxide, and potassium ethoxide in absolute ethanol with a key additive of acetic acid. Powder gels were obtained by exposing the solution to atmospheric water, thus hydrolysing the solution. The precursor powder crystallized to pyrochlore at 600 °C, and then completely transformed to perovskite at 750 °C. Alternatively, thin films were deposited on quartz glass, silicon, sapphire, yttria-stablized ZrO₂, LaAlO₃, SrTiO₃ and platinum-coated silicon plates, using the spinning technique. The crystal structure of the KTN thin films showed a strong dependency on the crystal structure of the substrates. Crack-free and transparent epitaxial KTN thin films were successfully prepared on SrTiO₃ (1 0 0) and (1 1 0) substrates and highly oriented KTN films on R-plane sapphire and LaAlO₃ (0 1 2) substrates. The chemical composition of the KTN powders and thin films is in good agreement with the atomic ratio of the starting materials. This revised version was published online in November 2006 with corrections to the Cover Date.     

Lead-free piezoelectric ceramics manufactured from tantalum-substituted potassium sodium niobate nanopowders

Nanopowders of lead-free (K_0.5Na_0.5)(Nb_0.9Ta_0.1)O₃ (KNNT) system were prepared by high-energy ball milling at different milling times keeping the milling speed fixed at 250 rpm. The particle size first decreases from 35 nm to 3 nm and then increases to 98 nm as the milling time increases in steps of 5 h from 10 h to 30 h. Without using any sintering aid, dense ceramics were formed by sintering the powders at 1050 °C for 1 h. With decreasing particle size of the starting nanopowders, the ceramics exhibit gradual increase in density from 93.1% to 95.8%, coercive field (E_c) from 10.9 kV/cm to 15.1 kV/cm, electromechanical coupling factor (k_p) from 35% to 48%, and piezoelectric charge constant (d₃₃) from 80 pC/N to 128 pC/N. The systematic changes observed in these parameters corroborate the observed increase in particle size as the milling time increases from 25 h to 30 h.     

Structure and piezoelectric properties of Cu-doped potassium sodium tantalate niobate ceramics

The Cu-doped (K_0.5Na_0.5)(Nb_0.95Ta_0.05)O₃ (KNNT) ceramics were prepared by the solid state reaction ceramic technique. The phase structure and the micro-morphology were analyzed by X-ray diffraction (XRD) and scanning electron microscope (SEM). There exhibits a single phase in perovskite structure, even the grain sizes increase with copper addition. The dielectric constant (ε), the planar mode electromechanical coupling factor (k_p), the piezoelectric coefficient (d₃₃), and the mechanical quality factor (Q_m) of KNNT ceramics with copper additive are 320–450, 0.21–0.41, 70–110 pC/N, 105–979, respectively.     

Structure and dielectric properties of potassium niobate nano glass–ceramics

Glasses in the composition of 25K₂O-25Nb₂O₅-50SiO₂ (mol %) have been prepared by melt quenching technique and isothermally heat-treated at 800 °C for different duration (0–200 h). The formed nanocrystalline KNbO₃ phase, crystallite size and morphology are examined by X-ray diffraction, Fourier transform infrared reflection spectroscopy, field emission scanning and transmission electron microscopes. The frequency and temperature dependent dielectric constant and loss tangent are measured in the frequency and temperature ranges 0.1–1000 kHz and 200–500 °C respectively. The dielectric constant and loss tangent are found to decrease with increasing frequency and increase with increasing temperature. The dielectric constant and loss tangent versus temperature curve at different frequency revealed the phase transition of KNbO₃ from paraelectric cubic to ferroelectric tetragonal around 425 and 397 °C (Curie temperature) for nano glass–ceramics obtained after 1 and 200 h heat-treatment respectively.     

Structural phase transitions of FeTi-deuterides

Absorption and desorption isotherms of FeTiD_x (0≤x≤1.9) were measured at room temperature. They indicate isotope effects. The dependence of the crystal structure of FeTiD_x on D₂-pressure (≤153 bar) was investigated at room temperature by means of neutron diffraction on powder samples both in absorption and desorption. The results show that the distribution of the deuterium atoms in the orthorhombic β-phase change from $\text{0.88}\text{0.12}$ for the DI/DII sites at x=1.0 (1) to $\text{0.92}\text{0.45}$ at x=1.4. This can be interpreted as a transition from a β₁-phase of composition FeTiD to a β₂-phase of approximate composition (FeTi)₃D₄. For the last composition Lebsanft (2) has reported a $\text{0.70}\text{0.70}$ distribution over the two D-sites. In agreement with (3) the structure of γ-FeTiD (x>1.9) is found to be monoclinic (space group $\text{P}\text{2}\text{m}$). Associated with considerable lattice expansions deuterium atoms occupy both in β- and γ-phases octahedral sites.     

Phase interface perturbations in phase transitions

The linear problem of viscous phase interface perturbations in intensive condensation/evaporation processes (at great transversal mass fluxes) is numerically solved. In limit cases, transition to the classic Helmholtz and Landau instability problems is ensured. The effects of viscosity, thermal conductivity, and surface tension are taken into account. The limit case of long-wavelength perturbations is considered using the method of matched asymptotic expansions.     

Instabilities in first order phase transitions

Majority of the metallurgical phase transformations are first-order transitions which occur by the nucleation and growth process near equilibrium conditions. In recent years, homogeneous transformation has been reported in some of these cases at conditions significantly away from those of equilibrium. In this paper some of these transformations will be discussed. In the first part of the presentation the thermodynamic and the mechanistic distinctions between first and higher order phase transformations will be discussed and a comparison made between homogeneous and heterogeneous modes of phase transformations and those of deformation. Based on Landau’s free energyvs generalised order parameter plots, an instability temperature is defined for first order phase transformations below which the transformation can occur by a continuous amplification of a concentration or a strain fluctuation. In the second part experimental evidence in support of the continuous mode of transformations in two ordering reactions are presented. These are: (i) a transition from the short range to the long range chemical order in Ni₄Mo (D1a structure) and (ii) a hybrid displacive-replacive ordering in Zr₂Al (B8₂ structure). In order to make the continuous mode operative in these first order transformations (which is possible at a high “supercooling”), radiation in the former and rapid quenching in the latter were employed. In the last part, the martensitic transformation and the shape memory effect is described in terms of Landau’s plots and the mechanical and thermodynamical consequences of the model are discussed. Only a summary is presented.