Thermal conductivity in the ferromagnetic metallic phase of monovalent Ag doped manganites

2014 ◽  
Vol 03 (03) ◽  
pp. 1450015
Author(s):  
Dinesh Varshney ◽  
E. Khan ◽  
Dinesh Choudhary
Keyword(s):  
Thermal Conductivity ◽  
Relaxation Rate ◽  
Acoustic Phonon ◽  
Phonon Scattering ◽  
Metallic Phase ◽  
Charge Carriers ◽  
Metallic State ◽  
Scattering Mechanism ◽  
Doped Manganites ◽  
Heat Carriers

The thermal conductivity (κ) behavior in La 0.75 Ag 0.25 MnO 3 manganites is investigated by probing the phonon, carrier and magnon scattering sources. The acoustic phonon contribution to the thermal conductivity (κph) is investigated within the Debye-type relaxation rate approximation. The scattering of phonon from defects, grain boundaries, charge carriers, and phonon are the major sources. La 0.75 Ag 0.25 MnO 3 witnesses the dominant κph and is artifact of strong phonon–impurity and phonon–phonon scattering mechanism in the ferromagnetic metallic state. The carrier contribution to the thermal conductivity (κe) is estimated following the Wiedemann–Franz law. In the metallic phase spin waves (κm) also shows the importance. It is noticed that κm increases with a T2 dependence on the temperature. The behavior of thermal conductivity (κ) in La 0.75 Ag 0.25 MnO 3 is determined by competition among the several operating scattering mechanisms for the heat carriers and a balance between electron, magnon, and phonon contributions.

EFFECT OF EMBEDDING NANOPARTICLES ON THERMAL CONDUCTIVITY OF CRYSTALLINE SEMICONDUCTORS: PHONON SCATTERING MECHANISM

2009 ◽  
Vol 08 (06) ◽  
pp. 551-556 ◽  
Author(s):  
K. K. CHOUDHARY ◽  
D. PRASAD ◽  
K. JAYAKUMAR ◽  
DINESH VARSHNEY
Keyword(s):  
Thermal Conductivity ◽  
Grain Boundaries ◽  
Lattice Thermal Conductivity ◽  
Present Model ◽  
Phonon Scattering ◽  
Scattering Mechanism ◽  
Temperature Dependent ◽  
Pure Crystal ◽  
Model Hamiltonian ◽  
Heat Carriers

We evolve a theoretical model for quantitative analysis of decrease in thermal conductivity (κ) by embedding ErAs nanoparticles in In0.53Ga0.47As crystalline semiconductors. The lattice thermal conductivity by incorporating the scattering of phonons with defects, grain boundaries, electrons, and phonons in the model Hamiltonian are evaluated. It is noticed that the ErAs nanoparticles provide an additional scattering mechanism for phonons. The embedding of ErAs nanoparticles in In0.53Ga0.47As crystalline semiconductors, the phonon scattering with point defects and grain boundaries become more efficient, which cause in the decrease of thermal conductivity up to half of its value of pure crystal. Conclusively, the temperature dependent of thermal conductivity is determined by competition among the several operating scattering mechanisms for the heat carriers. Numerical analysis of thermal conductivity from the present model shows similar results as those revealed from experiments.

THERMAL TRANSPORT OF MgB2 SUPERCONDUCTORS: INTERPLAY BETWEEN ELECTRON AND LATTICE-IMPURITY SCATTERING

2007 ◽  
Vol 21 (26) ◽  
pp. 4517-4536 ◽  
Author(s):  
DINESH VARSHNEY ◽  
M. NAGAR ◽  
K. K. CHOUDHARY
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Phonon Scattering ◽  
Theoretical Calculations ◽  
Impurity Scattering ◽  
Metallic Phase ◽  
Scattering Mechanism ◽  
S Wave ◽  
Lattice Contribution ◽  
Relaxation Time Approximation

We use the Kubo model to calculate the lattice contribution to the thermal conductivity (κph) in MgB 2 superconductors. The theory is formulated when heat transfer is limited by the scattering of phonons from defects, grain boundaries, charge carriers, and phonons. The lattice thermal conductivity in normal state of MgB 2 superconductors dominates and is an artifact of strong phonon-impurity and -phonon scattering mechanism. Later on, the electronic contribution to the thermal conductivity (κe) is calculated within relaxation time approximation for π and σ band carriers with s wave symmetry. Such an estimate sets an upper bound on κe and is about 30% of the total heat transfer at room temperature. The validity of the Wiedemann Franz law is also examined and an enhanced Lorenz number is obtained. Both these channels for heat transfer are clubbed and κ tot develops a broad peak at about 120 K, before falling off at higher temperatures weakly. The anomalies reported are well-accounted in terms of the scattering mechanism by phonon and electron with impurities. It is shown that the behavior of the thermal conductivity is determined by competition among the several operating scattering mechanisms for the heat carriers and a balance between electron and lattice contributions. The contribution of carriers toward κ is substantial and is due to the fact that the carriers are condensed and do not carry entropy. We include comparisons with other theoretical calculations on κe and available experimental data. The numerical analysis of heat transfer in the metallic phase of MgB 2 shows similar results as those revealed from experiments.

Analysis of Thermal Conductivity of LaFeAsO at Low Temperature

2014 ◽  
Vol 1047 ◽  
pp. 1-3
Author(s):  
Netram Kaurav ◽  
K.K. Choudhary
Keyword(s):  
Thermal Conductivity ◽  
Lattice Thermal Conductivity ◽  
Phonon Scattering ◽  
Phonon Frequency ◽  
Density Wave ◽  
Spin Density Wave ◽  
Charge Carriers ◽  
Scattering Mechanism ◽  
Lattice Contribution ◽  
Maximum Contribution

Thermal conductivity κ (T) of LaFeAsO is theoretically investigated below the spin density wave (SDW) anomaly. The lattice contribution to the thermal conductivity (κph) is discussed within the Debye-type relaxation rate approximation in terms of the acoustic phonon frequency and relaxation time below 150 K. The theory is formulated when heat transfer is limited by the scattering of phonons from defects, grain boundaries, charge carriers, and phonons. The lattice thermal conductivity dominates in LaFeAsO and is an artifact of strong phonon-impurity and-phonon scattering mechanism. Our result indicates that the maximum contribution comes from phonon scatters and various thermal scattering mechanisms provide a reasonable explanation for maximum appeared in κ (T).

Electron–phonon interaction in P-, As-, and Sb-doped germanium in the intermediate concentration region

1980 ◽  
Vol 58 (9) ◽  
pp. 1268-1274 ◽  
Author(s):  
V. Radhakrishnan ◽  
P. C. Sharma
Keyword(s):  
Thermal Conductivity ◽  
Conduction Band ◽  
Phonon Scattering ◽  
Metallic State ◽  
Deformation Potential ◽  
Concentration Region ◽  
Electron Phonon Interaction ◽  
Impurity Atoms ◽  
Intermediate Concentration ◽  
Electron Phonon Scattering

The electron–phonon scattering, in the analysis of low temperature thermal conductivity of n-type germanium, is studied in the intermediate donor concentration region. At low concentrations, below metal–insulator transition, the donor electrons are bound to the impurity atoms, and at high concentrations they are free in conduction band. The properties in the intermediate concentration are explained by Mikoshiba's "inhomogeneity model". According to this model, the electrons are in a mixed state both in non-metallic and metallic state. The electron concentrations in the non-metallic and metallic regions are calculated for each sample and the theory of both bound electron–phonon scattering and free electron–phonon scattering are applied. This theory of mixed electron–phonon scattering explains the thermal conductivity results of P-, As-, and Sb-doped germanium samples between 1 and 20 K for intermediate donor concentrations from 1.1 × 1017 to 5.6 × 1017 cm−3. The values of density-of-states effective mass are kept constant (= 0.22) without variation with temperature. The values of shear and dilatation-deformation potential constants are obtained from our calculations. The values of shear-deformation potential for the electrons in the bound region are found to be between 14 and 16 eV, while the values of dilatation-deformation potential are between 1 and 3.5 eV for the electrons in the conduction band and these values are in agreement with the experimentally measured values.

Synthesis and thermoelectric properties of tantalum-doped ZrNiSn half-Heusler alloys

2014 ◽  
Vol 07 (03) ◽  
pp. 1450032 ◽  
Author(s):  
Degang Zhao ◽  
Min Zuo ◽  
Zhenqing Wang ◽  
Xinying Teng ◽  
Haoran Geng
Keyword(s):  
Thermal Conductivity ◽  
Electrical Conductivity ◽  
Acoustic Phonon ◽  
Figure Of Merit ◽  
Room Temperature ◽  
Phonon Scattering ◽  
Heusler Alloys ◽  
Hot Press ◽  
Arc Melting ◽  
Hot Press Sintering

The Ta -doped ZrNiSn half-Heusler alloys, Zr 1-x Ta x NiSn , were synthesized by arc melting and hot-press sintering. Microstructure of Zr 1-x Ta x NiSn compounds were analyzed and the thermoelectric (TE) properties of Zr 1-x Ta x NiSn compounds were measured from room temperature to 823 K. The electrical conductivity increased with increasing Ta content. The Seebeck coefficient of Zr 1-x Ta x NiSn compounds was sharply decreased with increasing Ta content. The Hall mobility was proportional to T-1.5 above 673 K, indicating that the acoustic phonon scattering was predominant in the temperature range. The thermal conductivity was effectively depressed by introducing Ta substitution. The figure of merit of ZrNiSn compounds was improved due to the decreased thermal conductivity and increased electrical conductivity. The maximum ZT value of 0.60 was achieved for Zr 0.97 Ta 0.03 NiSn sample at 823 K.

THERMAL CONDUCTIVITY OF HIGH TEMPERATURE SUPERCONDUCTORS

1991 ◽  
Vol 05 (12) ◽  
pp. 2003-2035 ◽  
Author(s):  
MANUEL D. NUÑEZ REGUEIRO ◽  
DARÍO CASTELLO
Keyword(s):  
Thermal Conductivity ◽  
High Temperature ◽  
Transition Temperature ◽  
Phonon Scattering ◽  
High Temperature Superconductors ◽  
Low Energy ◽  
Disordered Materials ◽  
Superconducting Transition ◽  
Universal Pattern ◽  
Heat Carriers

We review and analyze the data on the thermal conductivity of both ceramic and single crystal samples of high temperature superconductors. A universal pattern can be extracted and interpreted in the following way: phonons are the main heat carriers in these materials, and in the high temperature range the thermal conductivity κ is almost constant due to phonon scattering against disorder; below the superconducting transition temperature κ increases as phonon scattering against carriers condensing into the superconducting state decreases and at still lower temperatures there is a region in which a T2 law is obeyed that most probably is due to resonant phonon scattering against low energy excitations, i.e. tunneling systems similar to those found in disordered materials. The origin of the relevant disorder is discussed.

scholarly journals Challenges in Improving Performance of Oxide Thermoelectrics Using Defect Engineering

2021 ◽  
Author(s):  
Jamil Ur Rahman ◽  
Gul Rahman ◽  
Soonil Lee
Keyword(s):  
Thermal Conductivity ◽  
Phonon Scattering ◽  
Electronic Device ◽  
Low Cost ◽  
Temperature Stability ◽  
Charge Carriers ◽  
High Concentration ◽  
Anion Vacancies ◽  
Cation And Anion Vacancies ◽  
Oxide Thermoelectric Materials

Oxide thermoelectric materials are considered promising for high-temperature thermoelectric applications in terms of low cost, temperature stability, reversible reaction, and so on. Oxide materials have been intensively studied to suppress the defects and electronic charge carriers for many electronic device applications, but the studies with a high concentration of defects are limited. It desires to improve thermoelectric performance by enhancing its charge transport and lowering its lattice thermal conductivity. For this purpose, here, we modified the stoichiometry of cation and anion vacancies in two different systems to regulate the carrier concentration and explored their thermoelectric properties. Both cation and anion vacancies act as a donor of charge carriers and act as phonon scattering centers, decoupling the electrical conductivity and thermal conductivity.

The Phonon Thermal Conductivity of a Single-Layer Graphene From Complete Phonon Dispersion Relations

2010 ◽  
Author(s):  
Yunfeng Gu ◽  
Zhonghua Ni ◽  
Minhua Chen ◽  
Kedong Bi ◽  
Yunfei Chen
Keyword(s):  
Thermal Conductivity ◽  
Acoustic Phonon ◽  
Phonon Scattering ◽  
Phonon Dispersion ◽  
Single Layer ◽  
Single Layer Graphene ◽  
Optical Phonons ◽  
Relaxation Rates ◽  
Phonon Thermal Conductivity ◽  
Transverse Acoustic

In this paper, the phonon scattering mechanisms of a single layer graphene are investigated based on the complete phonon dispersion relations. According to the selection rules that a phonon scattering process should obey the energy and momentum conservation conditions, the relaxation rates of combing and splitting Umklapp processes can be calculated by integrating the intersection lines between different phonon mode surfaces in the phonon dispersion relation space. The dependence of the relaxation rates on the wave vector directions is presented with a three dimensional surfaces over the first Brillion zone. It is found that the reason for the optical phonons contributing a little to heat transfer is attributed to the strong Umklapp processes but not to their low group velocities. The combing Umklapp scattering processes involved by the optical phonons mainly decrease the acoustic phonon thermal conductivity, while the splitting Umklapp scattering processes of the optical phonons mainly restrict heat conduction by the optical phonons themselves. Neglecting the splitting processes, the optical phonons can contribute more energy than that carried by the acoustic phonons. Based on the calculated phonon relaxation time, the thermal conductivities contributed from different mode phonons can be evaluated. At low temperatures, both longitudinal and in-plane transverse acoustic phonon thermal conductivities have T2 temperature dependence, and the out-of-plane transverse acoustic phonon thermal conductivity is proportion to T3/2. At room temperature, the calculated thermal conductivity is on the order of a few thousands W/m.K depending on the sample size and the edge roughness, which is in agreement with the recently measured data.

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