Optimizing Thermoelectric Efficiency of La_3-xTe₄ with Calcium Metal Substitution

Abstract

La 3-x Te 4 is a state-of-the-art high temperature n-type thermoelectric material with a previously reported maximum zT~1.1 at 1273 K. Computational modeling suggests the La atoms play a crucial role in defining the density of states for La 3-x Te 4 in the conduction band. In addition to controlling charge carrier concentration, substitution with Ca 2+ atoms on the La 3+ site is explored as a potential means to tune the density of states and result in larger Seebeck coefficients. High purity, oxide-free samples are produced by ball milling of the elements and consolidated by spark plasma sintering. Powder XRD and electron microprobe analysis are used to characterize the material. High temperature thermoelectric properties are reported and compared with La 3-x Te 4 compositions. A maximum zT of 1.3 is reached at 1273 K for the composition La 2.22 Ca 0.775 Te 4 .

Recent advances in high-performance bulk thermoelectric materials

“…21). 53,332,333 SnSe has an anisotropic layered orthorhombic structure. When cooling from high temperatures, SnSe undergoes a displacive phase transition at 750-800 K from the high symmetry phase with the space group Cmcm (#63) to the lower symmetry phase with the space group Pnma (#62) and a concomitant matrix transformation of its axes (Fig.…”

Uncovering the Structure and Stability of Thermoelectric La3–xTe4–Ni Composites Using High-Resolution and In Situ TEM

“…In contrast to bulk materials, the thermal and electrical conductivities in nano-thermoelectrics can be independently controlled by scaling down the size of the material. ,, Traditional thermoelectric materials (Si 1– x Ge x and PbTe) have moderate performance with device-level conversion efficiencies of 6–6.5%. New thermoelectric materials, such as n- and p-type filled skutterudites and rare-earth metal composites, however, have increased thermoelectric efficiencies by 2-fold when compared with traditional thermoelectrics . Various approaches have been scouted to enhance the thermoelectric efficiency by incorporating nanoparticles into the microstructure and improving grain refinements. − The concept of bulk nanocomposite thermoelectrics evolved as a result of combining the ideas of improved bulk and low-dimensional thermoelectric materials and, therefore, retain the superior characteristics of both of these counterparts that result in enhanced efficiency .…”

“…Computational studies of La 3– x Te 4 indicate that La plays a vital role in defining the density of states (DOS) in the conduction band, and the material possesses low κ l values and excellent electric transport properties at 1273 K. ,− The carrier density in La 3– x Te 4 is controlled by the vacancies of La, where La 3+ provides three electrons to the crystal structure and Te uses two of the three electrons to complete its valence. The stoichiometry of the La 3– x Te 4 crystal is shown below (La vacancies are denoted by V La ): At x = 0, there is one free electron per formula unit leading to degenerate semiconductor properties (formula: La 3 Te 4 ), and the introduction of La vacancies results in an intrinsic semiconducting behavior with no free electrons (formula: La 2.67 Te 4 ). , When La 3+ is substituted with a divalent metal cation (M 2+ ), the chemical environment changes as follows ( y denotes the number of substituted M 2+ cations): The substitution of La 3+ with divalent metal ions such as Ca 2+ and Yb 2+ has been explored in previous work where a better control over the carrier density with improved zT values (1.2–1.3 at 1273 K) was achieved. ,, A DFT study combined with Boltzmann transport theory explains that the band structure of La 3– x Te 4 has a strong influence on improved thermoelectric efficiency at temperatures above 1000 °C compared to legacy n-type thermoelectric materials. The Seebeck coefficient is enhanced due to the increased energy dependence of the DOS, which is explained by the sharp increase of the DOS ascribable to the presence of heavy bands in the energy-dependent analysis of the DOS ( N ( E )).…”

“…New thermoelectric materials, such as n-and p-type filled skutterudites and rareearth metal composites, however, have increased thermoelectric efficiencies by 2-fold when compared with traditional thermoelectrics. 13 Various approaches have been scouted to enhance the thermoelectric efficiency by incorporating nanoparticles into the microstructure and improving grain refinements. 14−16 The concept of bulk nanocomposite thermoelectrics evolved as a result of combining the ideas of improved bulk and low-dimensional thermoelectric materials and, therefore, retain the superior characteristics of both of these counterparts that result in enhanced efficiency.…”

“…The substitution of La 3+ with divalent metal ions such as Ca 2+ and Yb 2+ has been explored in previous work where a better control over the carrier density with improved zT values (1.2− 1.3 at 1273 K) was achieved. 3,13,28 A DFT study combined with Boltzmann transport theory explains that the band structure of La 3−x Te 4 has a strong influence on improved thermoelectric efficiency at temperatures above 1000 °C compared to legacy n-type thermoelectric materials. The Seebeck coefficient is enhanced due to the increased energy dependence of the DOS, which is explained by the sharp increase of the DOS ascribable to the presence of heavy bands in the energy-dependent analysis of the DOS (N(E)).…”