Decoupling the Electrical Conductivity and Seebeck Coefficient in the <i>RE</i>₂SbO₂ Compounds through Local Structural Perturbations

Compromise between the electrical conductivity and Seebeck coefficient limits the efficiency of chemical doping in the thermoelectric research. An alternative strategy, involving the control of a local crystal structure, is demonstrated to improve the thermoelectric performance in the <i>RE</i>₂SbO₂ system. The <i>RE</i>₂SbO₂ phases, adopting a disordered <i>anti</i>-ThCr₂Si₂-type structure (<i>I</i>4/<i>mmm</i>), were prepared for <i>RE</i> = La, Nd, Sm, Gd, Ho, and Er. By traversing the rare earth series, the lattice parameters of the <i>RE</i>₂SbO₂ phases are gradually reduced, thus increasing chemical pressure on the Sb environment. As the Sb displacements are perturbed, different charge carrier activation mechanisms dominate the transport properties of these compounds. As a result, the electrical conductivity and Seebeck coefficient are improved simultaneously, while the number of charge carriers in the series remains constant

Disorder-Controlled Electrical Properties in the Ho₂Sb_1–<i>x</i>Bi_<i>x</i>O₂ Systems

High-purity bulk samples of the Ho₂­Sb_1–<i>x</i>­Bi_<i>x</i>O₂ phases (<i>x</i> = 0, 0.2, 0.4, 0.6, 0.8, 1.0) were prepared and subjected to structural and elemental analysis as well as physical property measurements. The Sb/Bi ratio in the Ho₂­Sb_1–<i>x</i>­Bi_<i>x</i>O₂ system could be fully traversed without disturbing the overall <i>anti</i>-Th­Cr₂Si₂ type structure (<i>I</i>4/<i>mmm</i>). The single-crystal X-ray diffraction studies revealed that the local atomic displacement on the Sb/Bi site is reduced with the increasing Bi content. Such local structural perturbations lead to a gradual semiconductor-to-metal transition in the bulk materials. The significant variations in the electrical properties without a change in the charge carrier concentration are explained within the frame of the disorder-induced Anderson localization. These experimental observations demonstrated an alternative strategy for electrical properties manipulations through the control of the local atomic disorder

Refined Synthesis and Crystal Growth of Pb₂P₂Se₆ for Hard Radiation Detectors

The refined synthesis and optimized crystal growth of high quality Pb₂P₂Se₆ single crystals are reported. Improved experimental procedures were implemented to reduce the oxygen contamination and improve the stoichiometry of the single crystal samples. The impact of oxygen contamination and the nature of the stoichiometry deviation in the Pb₂P₂Se₆ system were studied by first-principles density functional theory (DFT) electronic structure calculations as well as experimental methods. The DFT calculations indicated that the presence of interstitial oxygen atoms (O_int) leads to the formation of a deep level located near the middle of the gap, as well as a shallow acceptor level near the valence band maximum. In addition, total energy calculations of the heat of formation of Pb₂P₂Se₆ suggest that the region of thermodynamic stability is sufficiently wide. By refining the preparative procedures, high quality Pb₂P₂Se₆ single crystal samples were reproducibly obtained. These Pb₂P₂Se₆ single crystals exhibited excellent optical transparency, electrical resistivity in the range of 10¹¹ Ω·cm, and a significant increase in photoconductivity. Infrared photoluminescence of the Pb₂P₂Se₆ single crystals was observed over the temperature range of 15–75 K. Detectors fabricated from boules yielded a clear spectroscopic response to both Ag Kα X-ray and ⁵⁷Co γ-ray radiation. The electron and hole mobility-lifetime product (μτ) of the current Pb₂P₂Se₆ detectors were estimated to be 3.1 × 10^–4 and 4.8 × 10^–5 cm²/V, respectively