Improved thermoelectric performance in p-type Bi_(0.48)Sb_(1.52)Te_3 bulk material by adding MnSb_2Se_4

Bismuth telluride（Bi2Te3） based alloys, such as p-type Bi（0.5）Sb（1.5）Te3, have been leading candidates for near room temperature thermoelectric applications. In this study, Bi（0.48）Sb（1.52）Te3 bulk materials with MnSb2Se4 were prepared using high-energy ball milling and spark plasma sintering（SPS） process. The addition of MnSb2Se4 to Bi（0.48）Sb（1.52）Te3 increased the hole concentration while slightly decreasing the Seebeck coefficient, thus optimising the electrical transport properties of the bulk material. In addition, the second phases of MnSb2Se4 and Bi（0.48）Sb（1.52）Te3 were observed in the Bi（0.48）Sb（1.52）Te3 matrix. The nanoparticles in the semi-coherent second phase of MnSb2Se4 behaved as scattering centres for phonons,yielding a reduction in the lattice thermal conductivity. Substantial enhancement of the figure of merit, ZT, has been achieved for Bi（0.48）Sb（1.52）Te3 by adding an Mn（0.8）Cu（0.2）Sb2Se4（2mol%） sample, for a wide range of temperatures, with a peak value of 1.43 at 375 K, corresponding to -40% improvement over its Bi（0.48）Sb（1.52）Te3 counterpart. Such enhancement of the thermoelectric（TE） performance of p-type Bi2Te3 based materials is believed to be advantageous for practical applications.

Theoretical study on residual infrared absorption of Ti:sapphire laser crystals

Residual infrared absorption is a key problem affecting the laser emission efficiency of Ti:sapphire crystal.In this paper,the origin of residual infrared absorption of Ti:sapphire crystal is systematically studied by using the first principles method.According to the contact conditions of O octahedron in the crystal structure of Al_(2)O_(3),four Ti^(3+)−Ti^(3+)ion pair models and three Ti^(4+)−Ti^(3+)ion pair models were defined and constructed.For what we believe is the first time,the near-infrared absorption spectra consistent with the experimental results were obtained in specific theoretical models.The electronic structures,absorption spectra,and charge distributions calculated show that the line-contact Ti^(3+)−Ti^(3+)ion pair with antiferromagnetic coupling and the facecontact Ti^(4+)−Ti^(3+)ion pair are two main contributors to the residual infrared absorption of Ti:sapphire,while some other ion pair models provide a basis to explain more complex residual infrared absorption.