Thermoelectrical properties of(FeNi)_xCo_(4-x)Sb_(12) prepared by MA-SPS

Bulk skutterudite （FeNi）xCo4-xSbl2 with x varying from 0.05 to 1.0 were prepared by mechanical alloying and spark plasma sintering （MA-SPS）. The phases of the samples were analyzed by X-ray diffraction, and their thermoelectrical properties were tested by electrical constant instrument and laser thermal constant instrument. The experimental results show that bulk （FeNi）xCo4-xSb12 have the characteristic of typical semiconductor electricity. The addition of FeNi improves the electrical properties to a large extent; the samples of bulk （FeNi）xCo4-xSbl2 （x = 0.05-1.0） are n-type semiconducting materials; the increase of FeNi content can decrease the absolute value of Seebeck coefficient and therefore decrease the ZT value; FeNi with a higher content when x 〉 0.5 leads to an evident increase in thermal conductivity and also a decrease in ZT value. In general, for ZT value, the optimal added content of FeNi is 0.25-0.5 and the maximum ZT value is 0.2467 when x = 0.5 at 500℃.

Enhanced electrical transport performance through cation site doping in Y-doped Mg_(3.2)Sb_(2)

Mg_(3)Sb_(2)-based alloys are promising thermoelectric materials through n-type doping in Mg-rich growth conditions to overcome their intrinsic p-type behavior.First principle calculations are employed to investigate the dopant formation energy and electronic structures of Y-doped Mg_(3)Sb_(2).Results indicate that the Y atom is more favorable for substitution at the cation site.Simultaneously,the flattened band structure and increased density of state near the Fermi level of Y-doped Mg_(3)Sb_(2) indicate an enhanced electronic transport performance.The carrier concentration rises to 5.31×10^(19) cm^(-3) at room temperature,resulting in a significant increased power factor for Mg_(3.17)Y_(0.03)Sb_(2).The available optimization of electrical transport contributes to excellent thermoelectric performance,and a peak ZT~0.83 at 773 K was achieved for Y concentration x=0.03 in Mg_(3.2-x)Y_(x)Sb_(2).This work provides an alternative measure for optimizing the thermoelectric performance of n-type Mg_(3)Sb_(2) alloys by cation site doping.

Thermoelectric properties of Ag-doped compound:Mg_(3-x)Ag_(x)Sb_(2)

Mg_(3)Sb_(2)-based thermoelectric materials have poor electrical conductivity which is the key to limit thermoelectric performance that need to be solved.Herein we tuned the carrier concentration of Mg_(3)Sb_(2)-based materials via Ag doping at the Mg sites(at two distinct crystallographic sites)to enhance the electrical performance.Mg_(3-x)Ag_(x)Sb_(2)(0≤x≤0.05)has been prepared successfully by vacuum suspension smelting plus Spark Plasma Sintering technique.Using the vacuum suspension smelting plus Spark Plasma Sintering method,we proved that Ag doping can precisely tune the electrical transport properties and accordingly enhance the power factor.Moreover,the Ag doping leads to a low lattice thermal conductivity due to phonons scattering,and the maximal thermoelectric figure of merit ZT for Mg_(3-x)Ag_(x)Sb_(2)reaches 0.66 at 773 K.

Effects of boron content on the microstructure and properties of B_(x)C-TiB_(2)(x=4.5,6.5 or 8.5)ceramic composites by the reactive spark plasma sintering

B_(x)C-TiB_(2)ceramic composites were fabricated via reactive spark plasma sintering using TiC and B as the raw materials.The impact of B/TiC mole ratios on the phase compositions,densification behaviors,microstructure,and mechanical properties of the ceramic composites were investigated.The results showed that the stoichiometry of‘B_(x)C’could be tailored by changing initial boron content and the obtained B_(4.5)C,B_(6.5)C and B_(8.5)C phases have the same crystal structure(R-3 m).The excess of B enhanced the reaction between TiC and B,which released a large amount of hot energy and promoted the densification of the composites.The TB8.5 composite sintered at 1900°C had the best comprehensive mechanical properties,with hardness and flexural strength of 40.36 GPa and 551 MPa,respectively.The formation of nano-sized TiB_(2)grains induced by reaction were beneficial for improving the mechanical properties of these composites.