Pressure-induced charge density wave phase in Ag2−δTe

Abstract

Considerable excitement was generated by the observation of large and linear positive magnetoresistance (MR) in non-magnetic silver chalcogenides. Renewed interest in these materials was kindled by the discovery that Ag2Te in particular is a topological insulator with gapless linear Dirac-type surface states. High-pressure x-ray diffraction studies, combined with first-principles electronic structure calculations, have identified three phase transitions as the pressure is increased: an isostructural transition identified with an electronic topological transition followed by two structural phase transitions. These recent studies were carried out on nominally stoichiometric Ag2Te. For the present work we have prepared single-phase self-doped Ag2-dTe samples with a well-characterized silver deficit (d = 2.0´10-4) for structural and electrical transport measurements over extended ranges of pressure (0-43 GPa), temperature (2-300 K) and magnetic field (0-9 T). The temperature dependence of the resistivity exhibits anomalous behavior at 2.3 GPa, slightly above the isostructural transition, which we postulate is due to Fermi surface reconstruction associated with a charge-density-wave (CDW) phase. The anomaly is enhanced by the application of a 9T magnetic field and shifted to higher temperature, implying that the electronic Zeeman energy is sufficient to alter the gapping of the Fermi surface. A peak in the pressure dependence of the resistivity and a sudden drop in the pressure dependence of the mobility, occurring at 2.3 GPa, provide additional evidence for a CDW phase at pressures slightly above the isostructural transition.

Enhanced Thermoelectric Performance of Nanostructured Nickel-Doped Ag2Te

“…Such MITs may be due to the change in structure, CDW phase transition, and electron–electron correlation; CDW transitions are usually associated with opening of a gap near the Fermi level. This is in line with earlier report on Ag 2 Te . There are changes in crystal structure across these CDW transitions, corresponding to perhaps to the lattice contraction as the chemical pressure.…”

“…Figure 2a−c shows the electrical resistivity ρ measured on the cold-pressed sintered pellets of Ag 2−x Ni x Te, x = 0−0.155 having mass density greater than 82% of the bulk value (8.2 g/ cm 3 ) (Table S1) over the T range of 5−300 K. The ρ of x = 0 shows a slight increase below ∼15 K but rises above it with an increase in T like a doped narrow-bandgap semiconductor due to perhaps slowly decreasing carrier concentration (n) and phonon scattering. 17 A similar feature of ρ for x = 0.015 with change in slope near 150 and 240 K and magnitude is seen (Figure 2a). These features, that is, upturn at low T, a broad hump in the mid-T range and a broad dip at higher temperature, become more pronounced and shift toward higher temperature with an increase in x, evolving the overall behavior from x = 0.015 to 0.055 quite dramatically (Figure 2a,b).…”

“…Figure 2a-c shows the electrical resistivity ρ measured on the cold-pressed sintered pellets of Ag2-xNixTe, x = 0 -0.155 having mass density greater than 82 % of the bulk value (8.2 g/cm 3 ) (table S1) over the T range of 5 K to 300 K. The ρ of x = 0 shows a slight increase below ~ 15 K but rises above it with increase in T like a doped narrow-bandgap semiconductor due to perhaps slowly decreasing carrier concentration (n) and phonon scattering 17 . Similar feature of ρ for x = 0.015 with change in slope near 150 K and 240 K, and magnitude is seen (figure 2a).…”

“…This is possible fortunately in nanostructures (NSs) by independently tuning the power factor (PF) S 2 σ and κ l as evident from, say, the size and morphology-controlled complex materials, 6 nanocomposites, 7,8 hybrid materials with inorganic/ organic interfaces, 9,10 introduction of nanoparticles (NPs) in the host matrix, 11 alloying, and doping. 12 Silver telluride (Ag 2 Te) is an interesting and attractive nonmagnetic topological insulator at ambient conditions 13,14 with many intriguing properties such as the structural phase transition from the low-temperature monoclinic phase β-Ag 2 Te to high-temperature face-centered cubic (fcc) phase α-Ag 2 Te near 417 K, 15,16 pressure-induced charge density wave (CDW) phase, 17 and structural 17,18 and electronic topological 19 phase transitions. While α-Ag 2 Te phase is a superionic conductor, its β-phase is a narrow-band gap (∼0.05 eV) semiconductor with high carrier mobility and low κ l due to the Ag-atoms-induced disordered structure in the Ag 2 Te lattice, 20 making it a suitable TE material.…”

Low Temperature Activation of Tellurium and Resource‐Efficient Synthesis of AuTe2 and Ag2Te in Ionic Liquids

“…[5] Silver telluride, Ag 2-δ Te, in its different phases is an ion conductor, a thermoelectric, a topological insulator and has a large magnetoresistance that can be exploited in magnetic field sensors. [6][7][8][9] The textbook example for the synthesis of Ag 2 Te is the reaction of solid silver with tellurium vapor at 475 °C. [10] Thin films are accessible by vacuum deposition of tellurium on chlorine activated silver films.…”