Theoretical prediction,synthesis,and crystal structure determination of new MAX phase compound V2SnC

Guided by the theoretical prediction,a new MAX phase V2SnC was synthesized experimentally for the first time by reaction of V,Sn,and C mixtures at 1000°C.The chemical composition and crystal structure of this new compound were identified by the cross-check combination of first-principles calculations,X-ray diffraction(XRD),energy dispersive X-ray spectroscopy(EDS),and high resolution scanning transmission electron microscopy(HR-STEM).The stacking sequence of V2C and Sn layers results in a crystal structure of space group P63/mmc.The a-and c-lattice parameters,which were determined by the Rietveld analysis of powder XRD pattern,are 0.2981(0)nm and 1.3470(6)nm,respectively.The atomic positions are V at 4f(1/3,2/3,0.0776(5)),Sn at 2d(2/3,1/3,1/4),and C at 2a(0,0,0).A new set of XRD data of V2SnC was also obtained.Theoretical calculations suggest that this new compound is stable with negative formation energy and formation enthalpy,satisfied Born-Huang criteria of mechanical stability,and positive phonon branches over the Brillouin zone.It also has low shear deformation resistance c44(second-order elastic constant,cij)and shear modulus(G),positive Cauchy pressure,and low Pugh’s ratio(G/B=0.500<0.571),which is regarded as a quasi-ductile MAX phase.The mechanism underpinning the quasi-ductility is associated with the presence of a metallic bond.

Flexible ternary carbon black/Bi_(2)Te_(3) based alloy/polylactic acid thermoelectric composites fabricated by additive manufacturing

Flexible ternary carbon black/Bi_(2)Te_(3) based alloy/polylactic acid(CB/BTBA/PLA)composites were fabricated by additive manufacturing and their thermoelectric properties were investigated from 300 K to 360 K.At 300 K,as the mass ratios of BTBAs in the composites increased from 38.5% to 71.4%,both the electrical conductivity and Seebeck coefficient of the composites increased from 5.8 S/cm to 13.3 S/cm,and from 60.2 mV/K to 119.9 mV/K,respectively,and the thermal conductivity slightly increased from 0.15 W m^(-1)K^(-1) to 0.25 W m^(-1)K^(-1),as a result,the ZT value of the composites increased from 0.004 to 0.023.As the temperature increased from 300 K to 360 K,the electrical conductivity of all the composites slightly decreased,while the thermal conductivity slowly increased,and a highest ZT value of 0.024 was achieved for the composites with 71.4% BTBAs at 320 K.Unlike traditional sterolithography,fused deposition modeling,selective laser melting,etc.,this additive manufacturing process can directly print the solutions which contain inorganic fillers and polymer matrixes into almost any designed intricate geometries of thermoelectric composites,therefore this process has great potential to be used for fabrication of flexible polymer based thermoelectric composites and devices.