Thermoelectric Properties of the Intermetallic Quasi-Two-Dimensional Layered Structure LiBe

Abstract

The electronic transport coefficients of LiBe for the intermetallic quasi-two-dimensional layered structure are evaluated by means of the semi-classical Boltzmann theory and the rigid band model. It has been found that the charge carrier concentration is about −0.0026 e/uc at low temperature (T = 50 K), then it decreases with increase of temperature to reach −0.0028 e/uc at 250 K. Above this temperature the charge carriers concentration increases rapidly to reach −0.00228 e/uc at 600 K. The negative sign shows that LiBe exhibits n-type conduction at a certain value of chemical potential (μ = E F). The calculated electrical conductivity (σ/τ) at μ = E F shows that at low temperatures (50 K) LiBe exhibits low σ/τ of about 1.318 × 1021 (Ω ms)−1, this value increases rapidly with an increase of temperature to be 1.389 × 1021 (Ω ms)−1 at 300 K. Above 300 K the σ/τ reach to the saturated value of about 1.389 × 1021 (Ω ms)−1. It has been found that LiBe possesses a thermo-power (S) of about −460 μV/K at 50 K, which decreases with increase of temperatures to reach −220 μV/K at around 350 K. Increasing the temperatures above 350 K lead to a decrease S to be −190 μV/K at 600 K. It is clear that at a certain value of chemical potential LiBe exhibits n-type conduction as it has negative S in the whole temperature range; this supports our previous observation about the charge carriers concentration. It is a remarkable finding that LiBe exhibits a large Seebeck coefficient, which is attributed to the non-zero density of states at the Fermi level. The electron thermal conductivity (κ e/τ) increased linearly with the temperature, and we observed that at low temperature LiBe exhibits low κ e/τ of about 0.2 × 1016 W/mKs at 50 K. A rapid increases in κ e/τ occurs as a result of increasing the temperature to reach 2.1 × 1016 W/mKs at 600 K. The obtained values of the power factor (S 2 σ/τ) as function of temperature show that at low temperature (50 K) LiBe possesses a high S 2 σ/τ of about 2.8 × 1010 mW/mK2, and with increasing the temperature a rapid reduction in the S 2 σ/τ occurs till 350 K to reach the value of about 0.5 × 1010 mW/mK2. Above this temperature LiBe exhibits almost a stable S 2 σ/τ of about 0.6 × 1010 mW/mK2 at 600 K. Also, we have calculated the transport properties as a function of chemical potential at the vicinity of E F (±0.15 eV above and below E F) for two different temperatures. In LiBe for the quasi-two-dimensional layered structure, the Li and Be atoms are packed in zig-zag layers along the y-axis. The Li and Be layers are puckered with square nets of Li and triangular nets of Be alternating with each others along the z-axis. Given that the LiBe system exhibits two-dimensional (2-D) doping behavior, it might be justifiable to study its transport properties; however, we would like to explore the unique transport behavior arising from its 2-D electronic structure.