Min Jin

Enhanced thermoelectric performance in n-type polycrystalline SnSe by PbBr2 doping

A series of PbBr2-doped polycrystalline SnSe samples were synthesized by melting and hot pressing. By PbBr2 doping, the carrier concentration of SnSe was increased to 1.86 × 1019 cm−3 from 2.41 × 1017 cm−3, resulting in an increased electrical conductivity of 40 ± 2 S cm−1 at 713 K while the undoped SnSe was only 5.1 ± 0.3 S cm−1. Meanwhile, the PbBr2-doped samples also exhibit a larger density of state effective mass (0.812m0). Therefore, a high power factor of 4.8 ± 0.5 μW cm−1 K−2 and a peak ZT of 0.54 ± 0.1 were achieved at 793 K perpendicular to the hot pressing direction.

Mechanical properties anisotropy of PZNT93/7 single crystal

The mechanical properties of 93%Pb(Zn1/3Nb2/3)O3–7%PbTiO3 (PZNT93/7) single crystal were evaluated by microindentation and nanoindentation techniques. The (1 1 1) facet of the crystal exhibited excellent combination mechanical properties (Vickers microhardness Hv, fracture toughness Kc and elastic modulus Er) than those of (0 0 1) facet. The Hv on (1 1 1) and (0 0 1) facets were 3.71 GPa and 3.00 GPa, respectively. In-plane fracture toughness anisotropy was observed on both the (1 1 1) and (0 0 1) facets, the Kc value was low in the direction parallel to the domain wall but large in the direction perpendicular to it. The Er of (0 0 1) and (1 1 1) facets was independent of the load, Er(1 1 1) was measured to be about 130 GPa and Er(0 0 1) was about 110 GPa. The above results implied that (0 0 1) PZNT crystals would face a more severe challenge in device application due to their weaker combination mechanical properties but outstanding piezoelectric properties than those of (1 1 1) PZNT crystals.

EVALUATION OF PZNT FERROELECTRIC CRYSTALS GROWN BY DIFFERENT METHODS

ABSTRACT Relaxor ferroelectric (1−x)Pb(Zn1/3Nb2/3)O3-xPbTiO3(PZNT) crystals were grown from PZNT-PbO high temperature solution by flux Bridgman, bottom seeded solution growth (BSSG) and gas-cooling methods. PZNT wafers cutting from flux Bridgman and BSSG-grown crystals were homogenous while serious inclusions were observed in PZNT wafers grown by the gas-cooling method. The < 001 > -oriented PZNT crystals exhibited nearly the same dielectric/piezoelectric properties whatever the growth methods. However, the mechanical properties, such as Vickers Microhardness Hv and fracture toughness Kc of the crystal grown by gas-cooling method were much inferior. It was suggested that BSSG method is a potential approach for growing large-size and high-quality PZNT crystals.