A Review of Properties, Synthesis and Applications on Lanthanum Copper Oxychalcogenides

The study of layered materials has been a significant and fascinating area due to their unique physical and chemical properties. Among various layered materials, lanthanum copper oxychalcogenides (LaCuOX (X=S, Se, Te)) have drawn a lot of attention of researchers. The study of LaCuOX was initially focused on the optoelectronic performance due to its excellent optical and electronic properties. Recently, it was found that the layered LaCuOX material also exhibits good thermoelectric properties, providing an opportunity to achieve high energy conversion efficiency through the thermoelectric effects. In this report, an overview of recent advances in LaCuOX research is provided, including crystal and electronic structure, synthetic methods, physical properties, practical applications as well as some strategies to optimize their transport properties. Theoretical and experimental results on LaCuOX crystals or thin films are both discussed in this report. Finally, the challenges and outlook for LaCuOX are evaluated based on current progress.

Impact of Thermal Boundary Resistance on Thermoelectric Effects of the Blade-Type Phase-Change Random Access Memory Device

Phase-change random access memory (PCRAM) is widely regarded as one of the most promising candidates to replace Flash memory as the next generation of non-volatile memories due to its high-speed and low-power consumption characteristics. Recent advent of the blade-type PCRAM with low programming current merit further confirms its prospects. The thermoelectric effects existing inside the PCRAM devices have always been an important factor that determines the phase-transformation kinetics due to a fact that it allows PCRAM to have electric polarity dependent characteristics. However, the potential physics governing the thermoelectric effects for blade-type PCRAM device still remains vague. We establish a three-dimensional (3D) electro-thermal and phase-transformation model to study the influences of thermal boundary resistance (TBR) and device scaling on the thermoelectric effects of the blade-type PCRAM during its “RESET” operation. Our research shows that the presence of TBR significantly improves the electric polarity-dependent characteristics of the blade-type PCRAM, and such polarity-dependent characteristic is found immune to the scaling of the device. It is therefore possible to optimize the thermoelectric effects of the blade-type PCRAM through appropriately tailoring the TBR parameters, thus further lowering resulting power consumption.

Electromotive Force Generated in All Materials under Temperature Difference

In this research, we investigate the thermoelectric effects of general materials. The results of this showed that an electromotive force was generated under a temperature difference between two points in materials. As no material has infinite electric resistance, an electromotive force is expected to be generated under a temperature difference in all materials. In conclusion, the thermoelectric effect generates an electromotive force. This electromotive force causes an electric current to flow, thereby generating a magnetic field.This magnetic field generates the Earth's magnetic field, triboelectricity, sunspots, and kinetic energy of celestial bodies.This temperature differential electromotive force also generates lightning and creates an ionosphere that reflects radio waves.

Electromotive Force Generated in All Materials under Temperature Difference

In this research, we investigate the thermoelectric effects of general materials. The results of this showed that an electromotive force was generated under a temperature difference between two points in materials. As no material has infinite electric resistance, an electromotive force is expected to be generated under a temperature difference in all materials. In conclusion, the thermoelectric effect generates an electromotive force. This electromotive force causes an electric current to flow, thereby generating a magnetic field. This magnetic field generates the Earth's magnetic field, triboelectricity, sunspots, and kinetic energy of celestial bodies. This temperature differential electromotive force also generates lightning and creates an ionosphere that reflects radio waves.

Spin-Thermoelectric Effects in a Quantum Dot Hybrid System With Magnetic Insulator

We investigate spin thermoelectric properties of a hybrid system consisting of a single-level quantum dot attached to magnetic insulator and metal electrodes. Magnetic insulator is assumed to be of ferromagnetic type and is a source of magnons, whereas metallic lead is reservoir of electrons. The temperature gradient set between the magnetic insulator and metallic electrodes induces the spin current flowing through the system. The generated spin current of magnonic (electric) type is converted to electric (magnonic) spin current by means of quantum dot. Expanding spin and heat currents flowing through the system, up to linear order, we introduce basic spin thermoelectric coefficients including spin conductance, spin Seebeck and spin Peltier coefficients and heat conductance. We analyse the spin thermoelectric properties of the system in two cases: in the large ondot Coulomb repulsion limit and when these interactions are finite.

Phonon Drag Thermopower in Silicene in Equipartition Regime at Room Temperature

Similar to graphene, zero band gap limits the application of Silicene in nanoelectronics despite of its high carrier mobility. In this article we calculate the contribution of electron-phonon interaction to thermoelectric effects in silicene. One considers the case of free standing silicene taking into account interaction with intrinsic acoustic phonons. The temperature considered here is at room temperature. We noticed that the contribution to thermoelectromotive force due to electron drag by phonons is determined by the Fermi energy. The explicit temperature dependence of the contribution to thermoelectromotive force deriving from by phonons is weak in contrast to that due to diffusion, which is directly proportional to temperature. Thus a theoretical limit has been established for a possible increase of the thermoelectromotive force through electron drag by the intrinsic phonons of silicene. Keywords: Phonon-drag thermopower, electron-diffusion thermopower, silicene, fermi energy, zero band gap

Quantum Transport of Particles and Entropy

A unified view on macroscopic thermodynamics and quantum transport is presented. Thermodynamic processes with an exchange of energy between two systems necessarily involve the flow of other balancable quantities. These flows are first analyzed using a simple drift-diffusion model, which includes the thermoelectric effects, and connects the various transport coefficients to certain thermodynamic susceptibilities and a diffusion coefficient. In the second part of the paper, the connection between macroscopic thermodynamics and quantum statistics is discussed. It is proposed to employ not particles, but elementary Fermi- or Bose-systems as the elementary building blocks of ideal quantum gases. In this way, the transport not only of particles but also of entropy can be derived in a concise way, and is illustrated both for ballistic quantum wires, and for diffusive conductors. In particular, the quantum interference of entropy flow is in close correspondence to that of electric current.

Thermoelectric precession in turbulent magnetoconvection

We present laboratory measurements of the interaction between thermoelectric currents and turbulent magnetoconvection. In a cylindrical volume of liquid gallium heated from below and cooled from above and subject to a vertical magnetic field, it is found that the large-scale circulation (LSC) can undergo a slow axial precession. Our experiments demonstrate that this LSC precession occurs only when electrically conducting boundary conditions are employed, and that the precession direction reverses when the axial magnetic field direction is flipped. A thermoelectric magnetoconvection (TEMC) model is developed that successfully predicts the zeroth-order magnetoprecession dynamics. Our TEMC magnetoprecession model hinges on thermoelectric current loops at the top and bottom boundaries, which create Lorentz forces that generate horizontal torques on the overturning large-scale circulatory flow. The thermoelectric torques in our model act to drive a precessional motion of the LSC. This model yields precession frequency predictions that are in good agreement with the experimental observations. We postulate that thermoelectric effects in convective flows, long argued to be relevant in liquid metal heat transfer and mixing processes, may also have applications in planetary interior magnetohydrodynamics.

Spin thermoelectric effects on aluminum or phosphorus doped zigzag silicene nanoribbons

Based on the density-functional theory (DFT) combined with nonequilibrium Green’s function (NGF), this paper investigates the effects of either single aluminum (Al) or single phosphorus (P) atom substitutions at different edge positions of zigzag-edged silicene nanoribbons (ZGNRs) in the ferromagnetic state on the spin-dependent transport properties and spin thermoelectric effects. It has been found that the spin polarization at the Fermi level can reach 100% or –100% in the doped ZSiNRs. Meanwhile, the spin-up Seebeck effect (for -100% case) and spin-down Seebeck effect (for 100% case) are also enhanced. Moreover, the spin Seebeck coefficient is much larger than the corresponding charge Seebeck coefficient at a special doping position and electron energy. Therefore, the study shows that the Al or P doped ZSiNRs can be used to prepare the ideal thermospin devices.

Spin thermoelectric effects of new-style one-dimensional carbon-based nanomaterials

Based on first-principles methods, the authors of this paper investigate spin thermoelectric effects of one-dimensional spin-based devices consisting of zigzag-edged graphene nanoribbons (ZGNRs), carbon chains and graphene nanoflake. It is found that the spin-down transmission function is suppressed to zero, while the spin-up transmission function is about 0.25. Therefore, an ideal half-metallic property is achieved. In addition, the phonon thermal conductance is obviously smaller than the electronic thermal conductance. Meantime, the spin Seebeck effects are obviously enhanced at the low-temperature regime (about 80K), resulting in the fact that spin thermoelectric figure of merit can reach about 40. Moreover, the spin thermoelectric figure of merit is always larger than the corresponding charge thermoelectric figure of merit. Therefore, the study shows that they can be used to prepare the ideal thermospin devices.