Zi-Hao Wang

Raman investigation of lattice vibration modes and thermal conductivity of Nd-doped zircon-type laser crystals

Abstract The Raman spectra of neodymium-doped yttrium orthovanadate Nd:YVO 4 (NYV) and neodymium-doped gadolinium orthovanadate Nd:GdVO 4 (NGV) have been measured at room temperature with different geometrical configurations. On the basis of the group theory and lattice dynamics theory, all the Raman peaks are assigned, and a correlation between the thermal conductivity and the Raman scattering strength is presented. The thermal conductivity of Nd:GdVO 4 and Nd:YVO 4 crystals along [1xa01xa00] and [1xa00xa01] directions are calculated and a good agreement with experimental results is obtained. The higher thermal conductivity of NGV crystal is mainly attributed to the fact that the effective radius of Gd 3+ ion in NGV crystal is close to that of Nd 3+ ion, which in return, enhances the crystal field strength of the laser crystal.

Lattice vibration and absorbance of Er:Yb:YCOB single crystals

Abstract Er 3+ - and Yb 3+ -doped yttrium calcium oxoborate Er:Yb:YCa 4 O(BO 3 ) 3 (Er:Yb:YCOB) crystallizes with a fluorapatite-type structure in the monoclinic system. Its lattice vibrational modes were calculated by using space group theory, and Raman spectra were measured at room temperature with different scattering geometry projects. The experiments show that the characteristic lattice vibrational modes of Er:Yb:YCOB crystal arise mainly from the internal vibrations of the BO 3 , CaO 6 , and YO 6 groups. The three-dimensional network structure of Er:Yb:YCOB crystal is identified, and its excellent nonlinear optical (NLO) properties are mainly attributed to the BO 3 clusters that connects all the distorted YO 6 and CaO 6 octahedral clusters together. The combination of the strong absorption at 976 nm and the strong emission at 1537 nm makes this material very promising for use in an infrared laser system.

A Monte Carlo simulation on structure and thermodynamics of potassium nitrate electrolyte solution

Monte Carlo computer simulation of potassium nitrate solution is carried out in the concentration ranging from 0.3 to 7.0u2009molu2009l−1. The cation (K+) and solvent water molecules are regarded as the charged and dipolar hard sphere respectively, and a simple four-site model for the nitrate ion is adopted in this study. It is found that there is an abrupt decline in the pressure with increasing ion concentration at fixed temperature. In supersaturated solutions for temperatures of 303 and 333u2009K, a metastable state with negative pressures and a strong energy fluctuation are observed. Some large ionic clusters are observed in supersaturated solutions at a temperature of 333u2009K, and they are composed of an ionic chain with alternating sign which indicates the formation of crystallization morphology. With decreasing solution concentration, the ionic hydration number varies from 5–7 for cation K+ and 3.5–4.7 for anion NO , which is in good agreement with time-of-flight neutron diffraction results.

Two-body integrals for hard sphere fluid in the first coordination layer

Hard sphere is a commonly used reference fluid, its two-body integrals are of great significance in perturbation theory. However, in order to model the highly orientated strong interactions, such as associating and ionic solvating with perturbation theory, the upper limit of the two-body integral should be restricted within the first coordination layer instead of infinite. In this paper, the two-body integrals confined to the first coordination shell for hard sphere fluid are calculated, which might be useful in representing semi-bonding interaction, such as hydrogen bonding and ionic solvating and pairing.

Two-body integrals for hard sphere fluid based on Tang-Lu RDF expression

Abstract Two-body integral with hard sphere reference fluid is of significance in thermodynamic modelling with perturbation theory. In this paper, the two-body integral is recalculated by using Tang–Lu radial distribution function (RDF) expression, which is superior to P–Y RDF in representing the structure of hard sphere fluid in whole density region and especially in contact-distance region. It is found that the two-body integral values calculated with Tang–Lu RDF are between those of Larsen et al.’s and Henderson et al.’s, and their difference is negligible. In order to investigate the accuracy of two-body integrals, properties of Lennard–Jones fluid are calculated with B–H perturbation theory under local-compressible approximation and compared with computer simulation results. It is shown that the accuracy of internal energy and compressibility calculated with two-body integrals of this paper and with Larsen et al.’s are 6.78, 8.60, 6.85 and 9.08%, respectively for 170 computer simulation data. As a whole, the accuracy of the present two-body integral with Tang–Lu RDF is a little superior to that of Larsen et al.’s.

Large low-field magnetoresistance observed in heterostructure La0.7Ca0.3MnO3/Gd0.7Ca0.3MnO3 superlattices

La0.7Ca0.3MnO3(LCMO)/Gd0.7Ca0.3MnO3(GCMO) multilayers have been prepared by pulsed laser deposition. High-resolution transmission electron micrographs demonstrate that perfect hetero-epitaxial growth has been achieved in the LCMO/GCMO superlattices with strains. In the superlattices, the resistivity-peak temperature decreases with reducing the thickness of the LCMO layers. Large low field magnetoresistance (LFMR) of Delta rho/rho(H) = 278% is obtained at 78.5 K in a LCMO/CCMO superlattice when a magnetic field swept within +/- 3100 Oe. This result suggests that the interface strains between LCMO and GCMO layers may have influences on the magnetic transport properties and a suitable film structure could be used to increase the LFMR