Of Lab <sub> 6 </ Sub> Optical Properties From First Principles Calculations And Experimental Research

Lanthanum hexaboride (LaB6) as an excellent thermionic electron emission source combines unusual properties of both metals and ceramics. Like metals, it is a good thermal and electrical conductor. And like ceramics, it is elastically stiff, exhibits excellent chemical stability. The excellent properties mentioned above make it a technically important material. Recently, researches discovery that LaB6 nanopowder which has obvious absorbing and scattering effect to NIR due to the localized surface plasmon resonance (LSPR) of conduction electrons is believed to be a new energy-saving and heat-insulating material for use with windows. Many investigations have been focusing on it in the field of photoelectronics. The electronic structure, optical properties and electronic structures under temperature or press of LaB6 were investigated theoretically by using the first-principle density function theory ab initio molecular dynamics method based upon the Density Functional Theory (DFT) using the CASTEP package of in this thesis. In addition, the synthesis of LaB6 nanopowder by solid-state reaction at a low temperature through microwave heating was studied. Meanwhile, PVB coatings containing LaB6 nanopowder was prepared and the optical performance was investigated. The main contents are as the following:1. The electronic structure and optical properties of LaB6 have been calculated using the first-principle density function theory.1) The calculations of band structure show that CaB6 is a conductor material.The density of state is mainly composed of La 5d 6s and B 2p. The static dielectric functionε1(0) is 213.7; the reflectivity n(0) is 14.8, the minimum trough of absorption coefficient is 21585.2 cm-1 in the visible light region; Moreover, the complex dielectric functions, reflectivity, absorption, refractive index, energy loss function and extinction coefficient of LaB6 are analyzed in terms of calculated band structure and density of state.2) Theoretical transmittance of LaB6 is nearly equal to zero in the UV and NIR, but visible light transmittance is very higher and its shape looks like "a hanging bell"; Theoretical transmittance of LaB6 is nonlinear with its temperature, the maximum value of theoretical transmittance is 57.6% at 300K. The results offer theoretical data for the design and application of the optoelectronic material LaB6.3) The electronic structure and optical properties of LaB6 is calculated at press, the results show that optical properties of LaB6 changes abruptly when the external pressure increases to a certain extent.4) The essential difference of optical properties of LaB6 and CaB6 depends on La 5d and Ca 3d of its own electronic structure which make contribution on themselves.2. Polyvinyl butyral resin (PVB) transparent thermal insulation coatings containing LaB6 nanoparticles were obtained by coating method. When the ratio of LaB6 is 0.05%, the transmittance is about 79% at visible light zone (380-780 nm) and the shielding efficiency of near-infrared radiation (780-1000 nm) was 54%, thus the PVB coatings containing LaB6 nanoparticles can block near infrared radiation. The temperature of the chamberloaded with the insulating glass was lower than that of the one with the conventional glass for 2.5℃under the irradiation of iodine-tungsten lamp for 60 minutes. Thus LaB6 nanoparticles can significantly reduce solar heat gain.