Metrological aspects of thermal relaxation technique by radiation loss for volumetric heat capacity measurements

One of the best-known methods to measure the heat capacity of solids consists in the illumination of the sample and the analysis of the thermal relaxation when the illumination is stopped. In this work, the energy balance equation with heat losses due to radiation is solved exactly. This is used to establish the limits of the usual approximations used to obtain the heat capacity from the experimental data. It is shown that large temperature changes, induced by the heat source during the experiment can generate errors in the calculation of heat capacity when the traditional approach is used.     

A further contribution to the theory of the transient hot-wire technique for thermal conductivity measurements

We study the density of states of a one-dimensional tightbinding electron model with random hopping elements. The Hamiltonian is $\text{H = -∑}{}_{\mathrm{i}}\text{J}{}_{\mathrm{<mtext>i+</mtext><mtext>1</mtext><mtext>2</mtext>}}\text{(a}{}^{\mathrm{+}}{}_{\mathrm{i}}\text{a}{}_{\mathrm{i+1}}\text{+a}{}^{\mathrm{+}}{}_{\mathrm{i+1}}\text{a}{}_{\mathrm{i}}\text{)}$, where the $\text{J}{}_{\mathrm{<mtext>i+</mtext><mtext>1</mtext><mtext>2</mtext>}}$'s are independent identically distributed random variables. It is proved that the single particle density of states D(E) diverges near E = 0 as $\text{1}\text{|(E}\text{log}{}^3\text{|E|)|}$.     

Improved thermal relaxation method for the simultaneous measurement of the specific heat and thermal conductivity

A novel method for the simultaneous, high-resolution measurement of the specific heat c and the thermal conductivity κ is presented. A new experimental setup has been developed with special emphasis on the elimination of systematic errors arising from radiative heat loss. A self-consistent data evaluation method is implemented which takes the effects of the sample geometry on c and κ properly into account. The measurements were performed over a broad temperature regime from 3 K up to room temperature on three compounds from the family of strongly correlated electron systems. The differences in their thermal properties and their highly sample-dependent sizes and shapes demonstrate the extended scope of the proposed method.     

Simultaneous determination of specific heat,thermal conductivity and thermal diffusivity at low temperature via the photopyroelectric technique

The photopyroelectric effect has been used to measure simultaneously specific heat (c), thermal conductivity (k) and thermal diffusivity () at low temperatures. A calibration procedure which allows the use of a pyroelectric transducer at low temperatures is described. Simultaneous measurements of c, k, and over a high T _c superconducting phase transition are reported.     

Relating phase transition heat capacity to thermal conductivity and effusivity in Cu2Se

Accurate measurement of thermal conductivity is essential to determine the thermoelectric figure‐of‐merit, zT. Near the phase transition of Cu₂Se at 410 K, the transport properties change rapidly with temperature, and there is a concurrent peak in measured heat capacity from differential scanning calorimetry (DSC). Interpreting the origin as a broad increase in heat capacity or as a transient resulted in a three‐fold difference in the reported zT in two recent publications. To resolve this discrepancy, thermal effusivity was deduced from thermal conductivity and diffusivity measurements via the transient plane source (TPS) method and compared with that calculated from thermal diffusivity and the two interpretations of the DSC data for heat capacity. The comparison shows that the DSC measurement gave the heat capacity relevant for calculation of the thermal conductivity of Cu₂Se. The thermal conductivity calculated this way follows the electronic contribution to thermal conductivity closely, and hence the main cause of the zT peak is concluded to be the enhanced Seebeck coefficient. (© 2016 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

A new technique for spatially resolved thermal lensing measurements

A new method is presented for spatially resolved thermal lensing measurements using multiple narrow probe beams and a two-dimensional array detector. The method is applied to an Er, Tm, Ho: YAG laser rod. No significant deviation from a parabolic temperature profile has been found although there is extraordinarily strong thermal lensing in the crystal. Thermo-optical constants of the material are reported.     

Low-temperature heat capacity and heat conductivity of single-crystal synthetic opals

The heat capacity at constant pressure (in the range 3–50 K) and the lattice heat conductivity (from 5 to 75 K) of a single-crystal synthetic opal are measured. It is shown that the heat capacity of the opal behaves at these temperatures in a way similar to porous amorphous materials. The data on the heat conductivity suggest that single-crystal opals can be related to a class of semicrystalline (partially crystallized amorphous) materials. However, because of specific features of their crystal structure, the opals form a nonstandard type of semicrystalline material which we termed semiamorphous.     

热线法测量材料热导率

讨论在SHT-20型热物性自动测量仪上,用热线法测量材料热导率的原理和方法,并给出了测量结果.     

Comparative study of textured diamond films by thermal conductivity measurements

Superior thermal conductivity, high resistance, high breakdown voltage and wide band gap make diamond an attractive material for a variety of applications in electronics. One of its most appealing applications is as a buried dielectric in silicon-on-diamond (SOD) technology. This paper presents thermal conductivity measurements conducted on a series of diamond films (grown by the microwave plasma chemical vapor deposition technique) as a function of the sample morphology and thickness, for eventual incorporation in the SOD structures. Results show that there is a significant difference in the measured thermal conductivity between samples with fiber texture and samples with sheet texture. Also, measurements performed on a 160-μm-thick diamond sample before and after reactive ion etching of approximately 10 μm of the nucleation layer show no significant change in the measured value of the thermal conductivity. PACS 81.05.Uw; 65.40.-b; 61.72.-y     

Electronic heat capacity and conductivity of gapped graphene

It investigated the effects of orderly substituted atoms on density of states, electronic heat capacity and electrical conductivity of graphene plane within tight-binding Hamiltonian model and Green's function method. The results reveal a band gap in the density of states, leading to an acceptor or donor semiconductor. In the presence of foreign atoms, the heat capacity decreases (increases) before (after) the Schottky anomaly. Moreover, the electrical conductivity of the gapped graphene reduces on all ranges of temperature compared to the pristine case. Deductively, all changes in the electronic properties depend on the difference between the on-site energies of the carbon and replaced atoms.     

A method for determining the static conductivity of semiconductor transparent heat mirrors

A simple method for determining the static conductivity of semiconductor transparent heat mirrors is developed that is based on the relationships of Drude theory and high-frequency optical measurements. The method consists of two steps. In the first step, the dielectric permittivity of the lattice ε_L and the plasma wavelength λ_p of the semiconductor film (a part of the heat mirror) are determined graphically using the reflectance measured at extreme points of interference fringes that are observed in the transparency regions of the reflectance spectra. The second step consists in the numerical computation of relaxation times and the static conductivity using the derived values of ε_L and λ_p and an experimental value of total emittance. The method was tested with transparent heat mirrors based on films of tin-doped indium oxide.     

Infrared thermography protocol for simple measurements of thermal diffusivity and conductivity

An accurate characterization of thermal properties requires the knowledge of both thermal diffusivity and conductivity. Most of the time, the thermal conductivity have to be measured with complicated setups. In this paper, we show that a combination of two experiments carried out with the same setup – stimulated infrared thermography – allows to estimate straightforwardly and quickly the absolute value of the thermal diffusivity and the thermal conductivity relatively to a reference material.     

真空热流法测定不良导体的导热系数

以恒定导热原理为基础,选用由温度表和温差电偶组成的温度测量装置,在真空环境下测量试样上下压杆对称位置的温度、有效传热面积和试样的厚度,通过计算机计算试样的导热系数.与传统的稳态法比较,采用真空热流法测定导热系数,材料内部的温度分布很快达到稳定,可以减小测量过程中试样及上加热盘和下散热盘侧面散热产生的影响.     

Thermal conductivity and heat capacity of cyclohexane under pressure

The transient hot-wire technique was used to determine the thermal conductivity, λ, and the specific heat capacity per unit volume, pc_p, of cyclohexane up to 1.5 GPa in the range 120–340 K. The measurements were carried out in a piston-cylinder apparatus, 45 mm in internal diameter, cooled by liquid nitrogen. There is only a small (6%) increase in λ on freezing, while there is an increase by a factor of two corresponding to the plastic→ normal crystal transition. The variation of λ with temperature (T) at P = 0.03 GPa is $\text{d(lnλ)}\text{dT}\text{= ?2.2×10}{}^{\mathrm{?3}}\text{K}{}^{\mathrm{?1}}$ for the liquid and $\text{d(ln λ)}\text{dT}\text{= ?0.9× 10}{}^{\mathrm{?3}}\text{K}{}^{\mathrm{?1}}$ for the plastic crystalline phase. In the norm crystal phase an approximate T^?1 dependence is observed. Within each of the phases λ increases linearly with pressure, and the slope of λ (P) is smallest in the plastic crystal phase. The existence of a recently reported new high pressure phase is evident from conductivity data. Qualitative ρC_p -results are reported.     

Heat capacity,electrical and thermal conductivity of silicene

We investigate the electronic heat capacity, electrical and thermal conductivity ofmonolayer planar and buckled silicon sheets (silicene) through tight binding approximationand Kubo-Greenwood formula. Applying and increasing dopant atoms to the system leads toopening a gap in the band structures and density of states that causes to decrease(increase) the heat capacity before (after) the Schottky anomaly. The electrical andelectronic thermal conductivity of doped silicene reduces with increasing impuritystrength.     

A mathematical method for optimizing the process of heat treatment with powerful laser

By using fast Fourier transform,a fast mathematical method based on the solu-tion of heat conduction equation is proposed in conditions of semi-infinite material with a sur-face heat source.It can be used to determine the temperature field or the ideal laser energyrepartition in treating material with powerful laser.     

Simultaneous measurement of thermal diffusivity,thermal conductivity and specific heat by impulse-response photopyroelectric spectrometry

A novel photothermal technique is developed, which enables the simultaneous measurement of the thermal diffusivity , thermal conductivity , and the specific heat C of a sample. The technique is based on frequency-modulated time-delay photopyroelectric spectrometry (FM-TDPS), which consists of chirped laser excitation of the sample and detection of the thermal impulse response by a thin-film pyroelectric detector. No calibration is required for the measurements; absolute values for , , and C may be obtained without having to employ a reference sample. Results on superconducting YBa₂Cu₃O_7–x are reported for the temperature range 50–300 K; the values obtained compare favorably with reported measurements of , , and C for YBa₂Cu₃O_7–x , which previously required separate experiments for their determination.