Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userTransport Properties of Cubic Crystalline Ge$_{2}$Sb$_{2}$Te$_{5}$: A Potential Low-temperature Thermoelectric Material
84
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
Ge$_{2}$Sb$_{2}$Te$_{5}$ (GST) has been widely used as a popular phase change material. In this study, we show that it exhibits high Seebeck coefficients 200 - 300 $mu$V/K in its cubic crystalline phase ($it{c}$-GST) at remarkably high $it{p}$-type doping levels of $sim$ 1$times$10$^{19}$ - 6$times$10$^{19}$ cm$^{-3}$ at room temperature. More importantly, at low temperature (T = 200 K), the Seebeck coefficient was found to exceed 200 $mu$V/K for a doping range 1$times$10$^{19}$ - 3.5$times$10$^{19}$ cm$^{-3}$. Given that the lattice thermal conductivity in this phase has already been measured to be extremely low ($sim$ 0.7 W/m-K at 300 K),citep{r51} our results suggest the possibility of using $it{c}$-GST as a low-temperature thermoelectric material.
rate research
Read More
We examine the ultrafast optical response of the crystalline and amorphous phases of the phase change material Ge$_2$Sb$_2$Te$_5$ below the phase transformation threshold. Simultaneous measurement of the transmissivity and reflectivity of thin film samples yields the time-dependent evolution of the dielectric function for both phases. We then identify how lattice motion and electronic excitation manifest in the dielectric response. The dielectric response of both phases is large but markedly different. At 800 nm, the changes in amorphous GST are well described by the Drude response of the generated photo-carriers, whereas the crystalline phase is better described by the depopulation of resonant bonds. We find that the generated coherent phonons have a greater influence in the amorphous phase than the crystalline phase. Furthermore, coherent phonons do not influence resonant bonding. For fluences up to 50% of the transformation threshold, the structure does not exhibit bond softening in either phase, enabling large changes of the optical properties without structural modification.
We report here an experimental and theoretical study on the magnetoresistance properties of heavily phosphorous doped germanium on the metallic side of the metal-nonmetal transition. An anomalous regime, formed by negative values of the magnetoresistance, was observed by performing low-temperature measurements and explained within the generalized Drude model, due to the many-body effects. It reveals a key mechanism behind the magnetoresistance properties at low temperatures and, therefore, constitutes a path to its manipulation in such materials of great interest in fundamental physics and technological applications
In search of better thermoelectric materials, we have systematically investigated the thermoelectric properties of a 122 Zintl phase compound EuCd$_{2}$As$_{2}$ using textit{ab-initio} density functional theory and semi-classical Boltzmann transport theory within constant relaxation time approximation. Considering the ground state magnetic structure which is A-type antiferromagnetic (A-AFM) and non-magnetic (NM) structure, we evaluated various thermoelectric parameters such as Seebeck coefficient, electrical and thermal conductivity, power factor and figure of merit (ZT) as function temperature as well as chemical potential. Almost all thermoelectric parameters show anisotropy between $xx$ and $zz$ directions which is stronger in case of A-AFM than in NM. Both A-AFM and NM phase of the compound display better thermoelectric performance when hole doped. We observed high Seebeck coefficient and low electronic thermal conductivity in A-AFM phase along $zz$ direction. The remarkably high ZT of 1.79 at 500 K in A-AFM phase and ZT$sim$1 in NM phase suggest that EuCd$_{2}$As$_{2}$ is a viable thermoelectric material when p-doped.
Using first-principles pseudopotential method and Boltzmann transport theory, we give a comprehensive understanding of the electronic and phonon transport properties of thermoelectric material BiCuSeO. By choosing proper hybrid functional for the exchange-correlation energy, we find that the system is semiconducting with a direct band gap of ~0.8 eV, which is quite different from those obtained previously using standard functionals. Detailed analysis of a three-dimensional energy band structure indicates that there is a valley degeneracy of eight around the valence band maximum, which leads to a sharp density of states and is responsible for a large p-type Seebeck coefficient. Moreover, we find that the density of states effective masses are much larger and results in very low hole mobility of BiCuSeO. On the other hand, we find larger atomic displacement parameters for the Cu atoms, which indicates that the stronger anharmonicity of BiCuSeO may originate from the rattling behavior of Cu instead of previously believed Bi atoms.
High mobility phonon-glass semimetal $CuAgSe$ has shown promise in recent years as a potential low-temperature thermoelectric material. It exhibits reasonably strong thermoelectric performance as well as an extremely high carrier mobility, both of which are enhanced when the material is doped with Ni at the Cu sites. The exact mechanism by which these enhancements result; however, is unclear. In order to further investigate the effects of chemical substitution on the materials thermoelectric properties, we have prepared and performed various measurements on $CuAgSe$ samples doped with Co and Cr according to the following compositional formulas: $Cu_{1-x}Co_{x}AgSe$ $(x=0.02, 0.05, 0.10)$ and $Cu_{1-x}Cr_{x}AgSe$ $(x=0.02, 0.05)$. Measurements of temperature and magnetic field dependent thermal conductivity, electrical resistivity, and Seebeck coefficient will be discussed. Our results reveal a remarkable sensitivity of $CuAgSe$s thermoelectric properties to chemical doping in general as well as a particular sensitivity to specific dopants. This demonstrated tunability of $CuAgSe$s various properties furthers the case that high mobility phonon glass-semimetals are strong candidates for potential low temperature thermoelectric applications.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
