High-thermoelectric performance of TiO_(2-x)fabricated under high pressure at high temperatures

We present the work about the initiative fabrication of multi-scale hierarchical TiO2-x by our strategy,combining high pressure and high temperature(HPHT)reactive sintering with appropriate ratio of coarse Ti to nanosized TiO_(2).Ubiquitous lattice defects engineering has also been achieved in our samples by HPHT.The thermoelectric performance was significantly enhanced,and rather low thermal conductivity(1.60 W m^(-1)K^(-1))for titanium oxide was reported here for TiO1.76.Correspondingly,a high dimensionless figure of merit(zT)up to 0.33 at 700℃was realized in it.As far as we know,this value is an enhancement of 43%of the ever best result about nonstoichiometric TiO_(2)and the result is also exciting for oxide thermoelectric materials.The moderate power factor,the significantly reduced thermal conductivity and the remarkable synergy between electrical properties and thermal conductivity are responsible for the excellent thermoelectric performance.We develop a facile strategy for preparing multi-scale hierarchical TiO_(2-x)and its superior ability to optimize thermoelectric performance has been demonstrated here.

Thermoelectric properties of In-substituted Ge-based clathrates prepared by HPHT

Bulk materials Ba_(8)Ga_(16)In_(x)Ge_(30-x)(x=0.5,1.0,1.5)were prepared by High-Pressure and High-Temperature(HPHT)method and the crystal structure has been confirmed by X-ray diffraction and cell refinement.The actual In composition was much lower than the starting composition,and lattice constants increased with the increase of substitution.As the temperature increased,the Seebeck coefficient and electrical resistivity increased first and then decreased,while the thermal conductivity was the opposite,which leads to significant enhancement on thermoelectric properties of the clathrates.The substitution of indium elements decreased the seebeck coefficient and electrical resistivity,and also changed the microstructure of the compounds.A minimum thermal conductivity of 0.84Wm^(-1)1K^(-1)was obtained,and a good ZT value of 0.52 was achieved.The grain boundaries and lattice defects generated by high pressure can effectively scatter phonons of different frequencies,which reduce the lattice thermal conductivity.