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The significance of the often observed kinetic compensation effect (KCE) remains controversial. The assumption of its validity, as well as its ubiquity, has led to speculations on its significance with no general consensus in the scientific community. Efforts to understand the KCE have usually attempted connections between microscopic events, structures, and mechanisms involved in various kinetic processes. An alternative proposition, with no relation to specific mechanisms, is presented suggesting that there is no new conceptual physics in the KCE. An analysis of internal friction (IF) in the framework of linear response to weak perturbations highlights that the concomitant energy dissipation cannot exceed a maximum or peak value which depends solely on the anelastic properties of the material. The KCE is shown to be a consequence of this simple fact. This physical principle underpinning the KCE is able to explain its ubiquity because of its general nature beyond any specific kinetic rate mechanism. Examples of IF in different systems such as polycrystalline thermoelectric composites and Al bicrystals, which show evidence of the KCE, conform to this prediction. While the observation on Al bicrystals has previously been presented and interpreted as signaling a phase transition, the analysis presented here demonstrates the simpler alternative. A similar argument is presented to derive the KCE in the thermal desorption of gases, which involves kinetic processes unrelated to the above examples. It is proposed that a KCE can, in general, be deduced for any set of closely related relaxation processes having close peak values of energy dissipation. [ABSTRACT FROM AUTHOR]

Mechanical spectroscopy measurements are reported on rods of (Bi1−xSbx)2Te3 and (Bi1−xSbx)2(Te1−ySey)3 polycrystalline thermoelectric (TE) composite alloys produced by mechanical alloying and hot extrusion. Low internal friction (Q−1) and large stiffness coefficients obtained in the 293–573 K range corroborate the improved elastic properties of these hot extruded and highly textured polycrystalline materials that have enhanced TE properties. Their stiffness shows a quadratic (decreasing) temperature dependence, and the value for most composites is larger than that of conventional single-phase random alloys and hot extruded bismuth telluride. One particular damping mechanism in Q−1, believed to be due to grain boundary motion, is thermally activated at temperatures higher than 420 K. The prefactor of the Arrhenius law correlates with the activation enthalpy (Δh) for every composite. It varies exponentially with Δh for more than six orders of magnitude for activation enthalpies up to 0.9 eV. The observation of this enthalpy–entropy compensation effect results from the existence of a maximum in energy dissipation in a linear regime of weak perturbations. This simple explanation is proposed to apply to this ubiquitous effect which has been observed in many areas of physics, chemistry, and biology. [ABSTRACT FROM AUTHOR]

A model of the thermoelectric transport properties of hot extruded bulk polycrystalline (HEBP) n-type Bi2Te3 has been developed based on the marked anisotropy of its properties induced by extrusion. HEBP Bi2Te3 is a highly textured material that allows treating electrical and thermal transport in the plane perpendicular to the extrusion axis as approximately isotropic. The model of this transport is based on the simplified electronic density of states suggested by ab initio calculations of the band structure of crystalline Bi2Te3 near the band edges. The proposed model can also be applied to transport along the extrusion axis in a temperature range when there is only one limiting charge carrier scattering mechanism. It provides excellent accord to the Hall effect (perpendicular) and the Harman (along extrusion) measurement of mobility, and the Seebeck coefficient of HEBP n-type Bi2Te3 in the temperature range from ∼200 to 460 K. It can be concluded that acoustic phonon scattering provides the limiting scattering mechanism for this temperature range. The model is also applied to elucidate the important role of thermodiffusion, suggesting that the usual approach to experimentally obtain this contribution to the thermal conductivity can only give approximate rough estimates. [ABSTRACT FROM AUTHOR]

The incorporation of dopants in III-V compound semiconductor epilayers during chemical vapor deposition involves complex homogeneous and surface reaction kinetics and is expected to be an activated process. In particular, silicon is an element of choice for n-type doping of various III-V compound epilayers for which there is a wealth of data involving different growth and doping precursors. Kinetic arguments such as the role of multi-excitation entropy or quasi-equilibration at the growth interface during incorporation predict an enthalpy-entropy compensation effect (EECE), which is observed from compiled data for more than 14 orders of magnitude of the prefactor describing the activated incorporation rate. For this particular observation of the EECE, an explanation involving data pre-selection imposed by restrictive growth conditions may also be invoked. [ABSTRACT FROM AUTHOR]

We investigate the quasi-static magnetic behavior of ensembles of ferromagnetic nanoparticles consisting of MnP nanoclusters embedded in GaP(001) epilayers grown at 600, 650, and 700 °C. We use a phenomenological model, in which surface effects are included, to reproduce the experimental hysteresis curves measured as a function of temperature (120-260K) and direction of the applied field. The slope of the hysteresis curve during magnetization reversal is determined by the MnP nanoclusters size distribution, which is a function of the growth temperature. Our results show that the coercive field is very sensitive to the strength of the surface anisotropy, which reduces the energy barrier between the two states of opposite magnetization. Notably, this reduction in the energy barrier increases by a factor of 3 as the sample temperature is lowered from 260 to 120K. [ABSTRACT FROM AUTHOR]

GaP:MnP samples, which consist of GaP(001) epilayers with embedded MnP nanoclusters occupying approximately 7% of the epilayer volume, were grown at three different substrate temperatures (600, 650, and 700 °C) using metal-organic vapor phase epitaxy. Angle dependent ferromagnetic resonance (FMR) spectroscopy indicates that, in all samples, MnP clusters are crystallographically oriented along specific GaP directions and possess high magnetic anisotropy fields. FMR results also suggest that the growth temperature significantly modifies the distribution of clusters among the possible orientations. This is verified from the measured angular dependence of the remanent magnetization, which shows a different crystallographic orientation of the GaP:MnP effective magnetic easy axis for each growth temperature. Modeling of the remanent magnetization allowed the determination of the relative volume fraction of clusters corresponding to each MnP c-axis orientation at a given growth temperature. These results support our assumption that the clusters are monodomains and suggest that the growth temperature could eventually be used to adjust the magnetic properties of these GaP:MnP structures. [ABSTRACT FROM AUTHOR]

We report on the angular dependence of ferromagnetic resonance (FMR) of GaP(001) epilayers with embedded MnP nanoclusters (GaP:MnP) grown on a GaP(001) substrate using metal-organic vapor phase epitaxy (MOVPE). Angle dependent FMR spectra obtained at 292 K show several peaks and indicate a strong magnetic anisotropy. The measured angular dependence of resonance fields can be modeled assuming that the MnP clusters possess a strong biaxial magnetocrystalline anisotropy whose axes are oriented along specific GaP crystallographic directions. Dominant populations of MnP clusters have their b-axis along GaP [111] and [111] directions, while a smaller population has the b-axis along the GaP [001] direction. In comparison, angle dependent FMR spectra of a polycrystalline MnP thin film grown on a GaP(001) substrate using MOVPE suggest that the crystals b-axis is oriented favorably along the GaP [001] direction. [ABSTRACT FROM AUTHOR]