No abstract

Half-Heusler materials are promising candidates for high-temperature power generation and have relatively high lattice thermal conductivity compared to other thermoelectric material systems. In this work, we report novel p-type YbNiSbbased half-Heusler alloys with a low lattice thermal conductivity (∼3.6 W m −1 K −1 at 340 K) that resulted from their large Gruneisen parameter, low sound speed, and low Debye temperature. All YbNiSb-based alloys exhibit a high carrier mobility of 30−50 cm 2 V −1 s −1 at room temperature because of their relatively small effective mass. Importantly, the structural analysis reveals that Yb-rich Yb 1.3 Ni 0.9 Sb 0.8 exhibits Yb/Ni and Yb/Sb substitution, indicating a wide homogeneity region of the YbNiSb phase experimentally. The adjustable Yb and Ni contents in YbNiSb-based alloys can modify the band structure around the Fermi level and significantly affect electrical transport properties. Additionally, by doping Ta at Yb sites, the carrier concentration and lattice thermal conductivity of these alloys can be manipulated. Consequently, a peak zT value of 0.45 at 823 K was achieved for Yb 0.95 Ta 0.05 NiSb. Our work demonstrates that YbNiSb-based alloys are promising p-type thermoelectric materials and suggests the possibility of exploring novel thermoelectric alloys in rare-earth nickel pnictides via tuning their composition and crystal structure.

Due to their excellent piezoelectric properties, low dielectric losses, and environmental friendliness, lead-free piezoelectric ceramics are gradually taking the place of lead-based piezoelectric ceramics and widely applied in commercial electronic devices. [1][2][3][4][5][6][7][8] Among the numerous lead-free piezoelectric ceramics, BaTiO 3 (BT) has gained many attentions on account of its low cost, easy processing, and good temperature stability.Whether for the lead-free or lead-based piezoelectric ceramics, an effective method to acquire high piezoelectric properties is to adjust the composition of the material to the vicinity of the phase transition boundaries. [9][10][11][12][13][14] Paraelectric to ferroelectric phase transition or two ferroelectric phase transition could be induced by the compositions, resulting in the instablility of the polarization state. Therefore, the polarization direction could be easily rotated under external stress or electric field, so that high piezoelectric properties could be achieved. [15][16][17][18] As far as pure BT material is concerned, there are four phases as the temperature increases, which are rhombohedral (R), orthorhombic (O), tetragonal (T), and cubic (C) phases, respectively. The stability of domain state in BT depends on the crystal structure. [19] The phase transition temperature and phase boundary type of BT ceramics can be altered by substituting the isovalent cations of Ba or Ti. Ca ions are usually used to lower the O to R phase transition temperature (T O-R ) and the T to O phase transition temperature (T T-O ) by replacing the Ba ions. In contrast, Sn, Zr, and Hf substitutions for Ti ions can increase T O-R and T T-O . [20] The changes of T-O or O-R transition allow to prepare the ceramics, which present high piezoelectric performances, in a wide range of dopants' compositions at room temperature. Ajay Kumar Kalyani et al. revealed that 2 mol% of Sn could stabilize the coexistence of