Investigation Of Preparation And Thermoelectric Properties Of P-type SnSe-based Polycrystals With Texture

Tin selenide(Sn Se) compound has been regarded as one promising thermoelectric(TE) material. However, the ZT values of 0.3 ~ 0.6 for pristine polycrystalline Sn Se were much lower due to their poor electrical property(S2σ < 5 μWcm-1K-2). In order to rebuild the anisotropy of polycrystalline Sn Se, the zone-melting method(ZM), zone-melting combined with spark plasma sintering(ZM-SPS) and zone-melting followed by hot pressing(ZM-HP) were employed to prepare Sn Se compound and highly textured compound were obtained. The phase structure, fractured surfaces, texturation degree and TE performance were investigated by the X-ray diffraction(XRD), scanning electron microscopy(SEM), ULVAC ZEM-3, Netzsch LFA-457 and physical properties measurement system(PPMS). The TE performance of Ge-doped Sn Se polycrystals was explored as well. The main conclusions are as follows:1. All samples show a preferred orientation grown along the(400) plane. The orientation factor values of(400) plane, F(400), were calculated according to the Lotgering method. The calculated values of F(400) for ZM, ZM-SPS and ZM-HP Sn Se samples are 0.98, 0.66 and 0.41, higher than those from reported literatures(0.04 ~ 0.31).2. The power factor(S2σ) of ZM, ZM-SPS and ZM-HP samples at 823 K are 3.88μWcm-1K-2, 6.33 μWcm-1K-2 and 9.52 μWcm-1K-2, respectively. The S2σmax of ZM samples reaches 9.82 μWcm-1K-2, almost twice of the reported Sn Se based polycrystals. The electric transport property increases along with the elevated textured degree. The introduction of grain boundaries and the reduction of textured degree reduce the thermal conductivity effectively. The grain sizes for ZM, ZM-SPS and ZM-HP Sn Se samples are >250 μm, 50 ~ 70 μm and 50 ~ 100 μm, respectively; the corresponding thermal conductivity are 0.95 Wm-1K-1, 0.69 Wm-1K-1 and 0.69 Wm-1K-1, respectively. Texture modulation is an effective way to optimize thermoelectric performance for Sn Se polycrystals. The ZT values of ZM and ZM-SPS samples can reach 0.92 and 1.05.3. Ge doping may deteriorate the electric transport properties of Sn Se. The roomtemperature carrier concentration of Sn0.92Ge0.08 Se sample is 6.6 × 1016 cm-3, 22% of Sn Se prepared by ZM-HP, and the power factor at 823 K reduces from 3.88 μWcm-1K-2 to 1.87μWcm-1K-2.