Electrical, magneto-transport and significant thermoelectric properties of Te-rich ZrTe5+δ polycrystals

The transition metal pentatelluride ZrTe5 has been studied extensively due to high thermoelectric power factors for potential applications in low-temperature refrigeration devices. Recent studies reveal that the physical properties of ZrTe5 are strongly dependent on Te concentration. Here, we have synthesized the Te-rich ZrTe5+δ polycrystalline by direct solid-state reaction and systematically investigated the electrical, magneto-transport and thermoelectric properties. Temperature-dependent resistivity and magneto-transport characterizations substantiate that ZrTe5+δ is a p-type (hole-doped) semiconductor. Besides, Seebeck coefficient is positive and linearly increases with T when T is within 10–150 K, and saturated to 120 μV K−1. Remarkably, a significant figure of merit ZT is obtained (∼0.037 at T = 300 K), which is higher than those in polycrystalline ZrTe5 (∼0.026) and sister compound HfTe5 (∼0.016) measured at 300 K. The significant thermoelectric performance of ZrTe5+δ is attributed to its low electrical resistivity (∼5 mΩ·cm), relative low thermal conductivity (∼2.0 W·K−1·m−1) and moderate Seebeck coefficient (∼120 μV K−1) at 300 K. Our work demonstrates the defect engineering, through delicate synthesis method, is an effective way to improve the thermoelectric property of ZrTe5.