Influence of Spark Plasma Sintering Conditions on the Optical and Mechanical Properties of Spinel.

The influence of spark plasma sintering (SPS) conditions on the optical and mechanical properties of MgAl2O4 spinel was investigated for application to infrared windows as parts of military systems. The thermal conditions of SPS, including the temperature and heating rate, have a significant impact on optical and mechanical properties. This study shows that the formation and growth of abnormal grains cause mechanical degradation with an increasing SPS temperature. In-line transmittance (Tin) was affected by the heating rate due to changes in oxygen vacancy and carbon contamination in SPSed samples. The fabricated spinel exhibited excellent flexural strength of 401 MPa and an average mid-infrared transmittance of 84.8% in the range of 3-5 µm.

Preparation and thermoelectric properties of Ag-dispersed Bi0.5Sb1.5Te3.

Ag-dispersed Bi0.5Sb1.5Te3 was prepared successfully by silver acetate (AgOAc) decomposition and hot pressing. The Ag nanoparticles were well-dispersed in the Bi0.5Sb1.5Te3 matrix, and acted as phonon scattering centers effectively. The electrical conductivity increased systematically with increasing amount of Ag nanoparticle dispersion, whereas it decreased with increasing temperature similar to metals or degenerate semiconductors. All specimens had a positive Seebeck coefficient, which confirmed that the electrical charge was transported mainly by holes. The Seebeck coefficient of Bi0.5Sb1.5Te3 decreased with increasing temperature but its temperature dependence was changed by Ag dispersion. The power factor values for Ag-dispersed Bi0.5Sb1.5Te3 increased significantly due to the increase in effective carrier mass and were higher over the entire temperature range. The decrease in lattice thermal conductivity by Ag dispersion overcame the increase in electronic thermal conductivity. The thermoelectric figure of merit was enhanced remarkably over a wide temperature range of 323-523 K due to the high power factor and the maintenance of low thermal conductivity.

Thermoelectric properties of Cu-dispersed bi0.5sb1.5te3.

A novel and simple approach was used to disperse Cu nanoparticles uniformly in the Bi0.5Sb1.5Te3 matrix, and the thermoelectric properties were evaluated for the Cu-dispersed Bi0.5Sb1.5Te3. Polycrystalline Bi0.5Sb1.5Te3 powder prepared by encapsulated melting and grinding was dry-mixed with Cu(OAc)2 powder. After Cu(OAc)2 decomposition, the Cu-dispersed Bi0.5Sb1.5Te3 was hot-pressed. Cu nanoparticles were well-dispersed in the Bi0.5Sb1.5Te3 matrix and acted as effective phonon scattering centers. The electrical conductivity increased systematically with increasing level of Cu nanoparticle dispersion. All specimens had a positive Seebeck coefficient, which confirmed that the electrical charge was transported mainly by holes. The thermoelectric figure of merit was enhanced remarkably over a wide temperature range of 323-523 K.PACS: 72.15.Jf: 72.20.Pa.