Anomalies In Thermal Conductivity Research Articles

Anomaly in the relation between thermal conductivity and crystallinity of silicate glass-ceramics

Thermal conductivity is a key property of oxide glass, especially for building applications such as thermal insulation materials and windows or glazed facades. However, this property is difficult to be predicted since it depends on several factors such as the degree of order/disorder and porosity. Here, we report on the effects of crystallization, crystalline phase, and crystal size on the thermal conductivity of a melt-quenched silicate glass. These effects were studied by heat-treating the glass at the onset crystallization temperature for different durations to vary crystallinity in the samples. The results show a general increase in thermal conductivity with crystallinity and crystal size in the nano-range (<75 nm). The growth of devitrite and combeite phases in the glass has a great impact on the thermal conductivity. Interestingly, an anomaly of thermal conductivity is found, i.e., the thermal conductivity of the sample with a relatively low crystallinity of <15 % is reduced by >20 % compared to that of the pure glass phase. This may be attributed to the grain boundaries between amorphous and crystalline phases, which scatter the phonons and thus reduce the thermal conductivity. These results imply that nano-crystallization in window glass might be a useful way to reduce the heat loss from glazed facades in the building envelope.

Hybrid Rendering for Interactive Visualization of Mantle Convection.

In this article, we describe our system for visualizing convection in the Earth's mantle using hybrid rendering-a combination of interactive raytracing, raycasting, and conventional rasterization graphics. The dataset for the SciVis 2021 contest includes a velocity vector field and multiple scalar fields, such as temperature and thermal conductivity anomalies, which we display using isosurface raycasting, streamlines, and line integral convolution, among other techniques. We demonstrate how these methods can be used to explore the dataset, identify slabs, plumes, and stagnations, and detect the influence of 660-km depth endothermic phase transition and mid-mantle spin transition on the mantle dynamics.

Thermal Conductivity of Supercritical CO2-Saturated Coal

The present study reports the effective thermal conductivity (ETC) of supercritical (SC) CO2-saturated black coal sample at temperatures from (304.15 to 323.15) K and pressures up to 20 MPa using a steady-state guarded parallel-plate method. The expanded uncertainty of thermal conductivity, pressure, and temperature measurements at the 95 % confidence level with a coverage factor of k = 2 was estimated to be 4 % (in the range of regular behavior of the thermal conductivity) and 5–6 % (in the critical region of the saturated CO2), 0.1 %, and 30 mK, respectively. This uncertainty in ETC measurement does not include the uncertainty due to contact thermal resistance and radiative conductivity inherent in this method. The effect of critical anomaly of thermal conductivity and other thermodynamic properties of pure CO2 near- and supercritical conditions on the total measured values of the ETC of SC CO2-saturated coal was studied. The thermal conductivity behavior of pure SC CO2 in coal pores was interpreted based on finite-size scaling theory of critical phenomena.

Thermal properties of Pr2/3Sr1/3MnO3 manganites:PdO composites

In the present communication the results on thermal conductivity, Seebeck coefficient and specific heat of Pr2/3Sr1/3MnO3:PdO composites are reported. All the samples exhibit a pronounced anomaly in thermal conductivity (κ) at their respective Curie temperatures, TC of the samples. It is also observed that the overall magnitude of κ decreases with increasing Pd content. The observed reduction of the total k(T) is discussed with various thermal scattering mechanisms. The temperature-dependent Seebeck coefficient data S(T) in the high temperature region is analyzed within the framework of Mott's polaron hopping model. The analysis of low-temperature S(T) data reveals that the electron-magnon scattering contribution dominates the thermoelectric transport at low temperatures. The magnetic contribution for the CP and change in entropy (ΔS) during the magnetic phase transition is also evaluated.

Low-temperature thermal conductivity and boson peak in the glassy g-As&lt;sub&gt;2&lt;/sub&gt;S&lt;sub&gt;3&lt;/sub&gt;

Background: Thermal conductivity and heat capacity with low temperature anomalies, the Boson peak in the in glassy materials are still not clearly understood and are matter of debate. Materials and methods: We studied thermal conductivity in g-As 2 S 3 between 2 and 100 K, depends k(T) for cycles cooling and heating. Results: Thermal conductivity is weakly temperature k(T) dependent from 2 to 10 K showing a plateau region during both cooling and heating. The jump of value in k(T) dependence compare with cooling k(T) curves was found during heating g-As 2 S 3 . The values show that the jump of k(T) is greater than the accuracy of the measurement producing an appreciable deviation from k values taken during cooling. The appearance of hysteresis of k(T) during heating was found in range of temperature from 11 to 60 K. Difference curve of k(T) (heating minus cooling) is complex asymmetric peak in energy range from 1 to 10 meV and reproduces the experimental low-temperature Boson peak (BP). Intensity of it being proportional to the density of states (g (ω)) by the rule of g (ω) / ω2. Our spectroscopic theoretical and experimental studies of glass structure in cluster approximation have shown that the nature of excitations in the low frequency region of the spectrum might be originate from rich a variety of vibrational properties clusters vibrations resulting from atomic scale disorder. In order to understand how these low frequency-modes depended on system clusters size we focus of attention in this work on the modes which might have vibrational character and be involved in measured low temperature thermal conductivity anomalies and Boson peak in g- As 2 S 3 . Conclusion: In region the cryogenic temperatures in g-As 2 S 3 when heating and cooling first discovered hysteresis temperature dependence of the thermal conductivity k(T). In g-As 2 S 3 regardless of k(T) in the range of 3.6K to 10K (0,31-0,92 meV) confirmed the presence of «plateau» (tgα = 0).

Thermal Conductivity Anomalies of RECoO3 (RE = La–Nd) Related to Valency and Spin State of Co Ion

The thermal conductivities κ( T ) of Co- and La-site-substituted LaCoO 3 were measured and the origin of the κ( T ) peak was investigated. The sharp κ( T ) peak at approximately 30 K is strongly suppressed by the introduction of a small amount of Jahn–Teller (JT)-active Co 4+ ions because of Co-site substitution by divalent ions such as Ni 2+ and Cu 2+ , similarly to the La-site substitution by Sr 2+ . In contrast, the κ( T ) peak of samples with the Co-site substituted by tetravalent ions such as Sn 4+ and Zr 4+ , which introduce Co 2+ ions, moderately decreased. The temperature at which a small and broad κ( T ) peak in the Pr-containing RECoO 3 [rare-earth (RE) = La 1- y Pr y and Pr 1- z Nd z ] is also observable shifts from 110 K for RE = La 0.5 Pr 0.5 to 180 K for RE = Pr and Pr 0.5 Nd 0.5 , which corresponds to the spin-state transition temperature of Co 3+ ions.

Thermal Conductivity Anomalies Related to the Double-Bump ofResistivity in Nd0.7Sr0.3Mn1−xCrxO3

The temperature dependence of the thermal conductivity κ(T) andelectrical resistivity ρ(T) has been measured for perovskiteNd0.7Sr0.3Mn1−xCrxO3 (0.01⩽x⩽0.15)in the temperature range of 10–300 K. The double-bump featurein ρ(T) is observed for x = 0.08 and 0.10samples. Below the insulating-metallic transition temperature TIM,κ(T) shows a sharp increase and such an increase is depressedgradually by the increasing Cr content. While κ(T) displays ananomalous decrease around the temperature where the second bump of ρ(T) emerges. We suggest that the enhancement of κ(T) belowTIM is related to both phonons and magnons, the ferromagneticinteraction of Mn3+-O-Cr3+ should be super-exchangeinteraction rather than double-exchange interaction, and the Crdoping just weakens the DE interaction in this system.

Anisotropy of the transport properties of (TaSe 4) 2I

The thermoelectric power, electrical and thermal conductivity of the charge-density-wave compound (TaSe 4 ) 2 I have been investigated in the chain and perpendicular to chain directions. A strong anisotropy of free carriers and lattice contribution to the transport properties is observed in the temperature range 100-320 K. The results of thermal conductivity are in favour to the our previous explanation that there are residual anomalies in thermal conductivity resulting from the contribution of the charge density wave excitations.

Scattering of phonons by a spatially correlated system of Fe atoms and the low-temperature anomaly of thermal conductivity in HgSe:Fe crystals

The thermal conductivity κ of HgSe:Fe samples with various content NFe of Fe impurity was studied in the temperature range of 8–60 K. It was found that the dependence of the thermal conductivity κ on NFe is unconventional at low temperatures. For T<12 K, the value of κ first decreases with an increase in the Fe concentration up to NFe=5×1018 cm−3 and then increases and attains a maximum for NFe=(1–2)×1019 cm−3. A further increase in Fe concentration brings about a steady decrease in thermal conductivity. The electron-and phonon-related thermal conductivity of HgSe:Fe crystals with consideration of the effects caused by the ordering of trivalent Fe ions was analyzed. It is shown that both the electron-and phonon-related contributions to thermal conductivity at low temperatures are increasing functions of Fe concentration in the range of 5×1018<NFe<(1–2)×1019 cm−3. However, the electronic contribution is too small to account for the experimental increase in thermal conductivity. An analysis of the lattice contribution to thermal conductivity showed that an anomalous increase in thermal conductivity is caused by a reduction in the Rayleigh scattering of phonons by a system of Fe ions with mixed valence and is related to the spatial ordering of Fe3+ ions.

Low-Temperature Anomaly in Thermal Conductivity ofBi2Sr2Ca(Cu1−xNix)2O8: Second Superconducting Phase?

We report the discovery of a low-temperature anomaly in thermal conductivity of ${\mathrm{Bi}}_{2}{\mathrm{Sr}}_{2}\mathrm{Ca}({\mathrm{Cu}}_{1\ensuremath{-}x}{\mathrm{Ni}}_{x}{)}_{2}{\mathrm{O}}_{8}$ high-temperature superconductor. This anomaly manifests itself as a sharp reduction of the thermal conductivity of the samples at a temperature ${T}_{c}^{*}\ensuremath{\approx}200\mathrm{mK}$. The temperature dependence of the thermal conductivity changes dramatically from ${T}^{\ensuremath{\alpha}}$ with $\ensuremath{\alpha}$ between 1.6 and 1.75 above ${T}_{c}^{*}$ to $T$-linear behavior below it. Application of a small magnetic field suppresses the low-temperature anomaly. We propose that such behavior is consistent with a phase transition into a second bulk low-temperature superconducting state at ${T}_{c}^{*}$. The presence of a second superconducting state would constitute direct evidence for unconventional superconductivity in ${\mathrm{Bi}}_{2}{\mathrm{Sr}}_{2}{\mathrm{CaCu}}_{2}{\mathrm{O}}_{8}$. Within the suggested scenario, time-reversal symmetry is likely to be violated in the low-temperature phase.

Anisotropy of the thermal conductivity in blue bronze

We have measured the thermal conductivity of K 0.3MoO 3 (blue bronze) in the chain direction and in both perpendicular directions from 80 to 300 K. As expected, it shows an anisotropic behaviour in lattice contribution as well as in free carrier contribution. These results are in favor to our previous explanation that there are residual anomalies in thermal conductivity resulting from the contribution of low-frequency phasons of rather large velocities.

Thermal conductivity of solid oxygen.

This paper reports the results of the first measurements of the thermal conductivity of the \ensuremath{\alpha}, \ensuremath{\beta}, and \ensuremath{\gamma} phases of solid oxygen over the temperature range of 1--52 K. A simple qualitative analysis was performed to explain the observed anomalies in thermal conductivity, which manifested themselves by a jump at the \ensuremath{\alpha}-\ensuremath{\beta} transition, the anomalously weak temperature dependence in the \ensuremath{\beta} phase and an increase of the conductivity with temperature in the \ensuremath{\gamma} phase.

Thermal conductivity of the Y-Ba-Cu-O tetragonal structure: phase transitions and hysteresis behaviour

The authors present results of precise measurements of the thermal conductivity lambda of a non-superconducting sample of Y-Ba-Cu-O in the temperature range 1-300 K. Heating and cooling curves of lambda (T) exhibited clear hysteresis effects between 80 and 240 K, not previously reported. The temperatures at which the thermal conductivity anomalies appear were the same or close to those at which other anomalies were observed in superconducting samples. The results can be explained qualitatively if one assumes that the 1:2:3 phase is a spinodal decomposition mixture of two phases with different stoichiometry with respect to oxygen content and that a change in lattice dimensions takes place at about 80 K.

Thermal properties of amorphous materials at low temperatures

Recent investigations of X-ray diffraction and electron micrograph studies reveal high density clusters separated by density deficient regions (voids) in amorphous materials. The low temperature specific heat and the thermal conductivity anomalies are explained on the basis of such a structure for amorphous materials. It is a generalisation of Debye's theory applied to most of the amorphous solids in the temperature range from 0 to 10 K. The anharmonic effects lead to the observed temperature dependence of the sound velocity. The thermal conductivity between 0 and 2 K is due to thermal diffusion, the plateau observed between 2 and 20 K is a consequence of the decrease in thermal conductivity due to three phonon processes compensated by intercluster diffusion, while beyond this range it is due to excitations within a cluster limited by the size of a cluster. Further the model predicts the coefficient of expansion about 100 times that found in the corresponding crystalline solids. An experimental verification of this result can be a good test for the model.

Free convective heat transfer to supercritical carbon dioxide

Experiments on free convective heat transfer from electrically heated platinum wires and a platinum strip to supercritical carbon dioxide were performed for a wide range of bulk conditions. It is shown that heat transfer can be predicted by a conventional Nusselt-type correlation if the dimensionless numbers are based on integrated thermophysical properties in order to account for large changes in these properties. The anomaly of thermal conductivity has to be considered. Agreement between the experimental results and the correlation is within 10% even for very thin wires when for those a correction factor is introduced.

Numerical calculations of the perturbation of normal heat flow by topographic and local conductivity structure

A numerical method is used to investigate the effect of topographic and local thermal conductivity anomalies on near-surface heat flow for two-dimensional models. Heat flow associated with a sloping topographic structure is calculated. Also, the effects of a fault structure associated with the sloping topography are considered. Vertical and horizontal heat flow components are calculated alone; the surface of the earth as well as throughout the whole region of interest. The results indicate that surface heat flow is substantially affected by topographic relief and the horizontal heat flow component associated with topographic features can be large. Also, regional heat flow is greatly perturbed by local thermal conductivity anomalies and the effect of topographic features may be considerably modified by the subsurface structure.

On the critical anomaly of thermal conductivity near the λ-transition

The critical exponent α κ of the thermal conductivity for an m-component Bose system is evaluated for m large, by applying renormalization group techniques to the Kubo formula. The result gives α K = 0.264 γ ≃ 0.35 for d = 3, which explains well experimental data on 4He.

Thermal Conductivity in Two Simple Antiferromagnets: RbMnF3and MnF2

The magnetic field dependence of the thermal conductivity has been used to investigate the magnon contribution to the total heat current and the magnetoelastic coupling in the simple antiferromagnets RbMn${\mathrm{F}}_{3}$ and Mn${\mathrm{F}}_{2}$. The thermal-conductivity measurements on both RbMn${\mathrm{F}}_{3}$ and Mn${\mathrm{F}}_{2}$ show no evidence for magnon conductivity. The zero-field results for RbMn${\mathrm{F}}_{3}$ and Mn${\mathrm{F}}_{2}$ are explainable in terms of phonons and phonon-scattering mechanisms. Neither Mn${\mathrm{F}}_{2}$ nor RbMn${\mathrm{F}}_{3}$ exhibit an anomaly in the thermal conductivity due to phonon scattering by critical fluctuations in the spin system near ${T}_{N}$. The umklapp-process scattering masks the effect due to critical spin fluctuations. The thermal-conductivity data on RbMn${\mathrm{F}}_{3}$ show striking changes as a function of applied field strength and direction. The position in field of the thermal-conductivity anomalies correlate well with the model of sublattice magnetization rotation developed from antiferromagnetic resonance. While no complete explanation of all the data can be given, it is suggested that the coupling between nuclear spins, electronic spins, and phonons is responsible for the field-dependent conductivity.

On the Behavior of Thermal Conductivity near the Magnetic Transition Point

The anomaly of thermal conductivity at the magnetic transition point observed in certain magnetic crystals was treated theoretically using the correlation function expression for the thermal conductivity. The heat conduction by the spin system is shown to be negligible in the vicinity of the transition point. The phonon thermal conductivity was studied when the transition temperature is much smaller than the Debye temperature adopting a simple spin-phonon coupling derived by a consideration of the change of energy of the spin system caused by the strain due to a phonon. Processes involving creation and annihilation of a phonon as well as scattering were considered, and the anomalous temperature dependence of thermal conductivity at the transition point was understood in terms of the critical scattering of phonons by critical fiuctuations of the energy density of the spin system that is revealed in the specific heat of the spins. Cases with more general types of the spin-phonon interaction are briefly discussed. (auth)