Heat Conductivity Measurements Research Articles

Determination of Thermal Properties of Carbon Materials above 2000 °C for Application in High Temperature Crystal Growth

AbstractThis work reports on the determination of the heat conductivity of high temperature stable carbon materials in the temperature range well above 2000 °C where classic material characterization methods fail. Dense graphite (DG) materials as well as rigid and soft felt isolation (RFI/SFI) components have been investigated which are used during crystal growth of SiC by the physical vapor transport method (PVT) in the temperature regime of 2000 and 2400 °C. The applied materials characterization methods include low temperature physical heat conductivity measurements using laser flash analysis (LFA) in the temperature range 25–1200 °C, data extrapolation to elevated temperatures up to 2400 °C, and a correlation of heating processes and computer simulation of the temperature field of different hot zone designs. Using this approach, the calculated temperatures and experimentally determined values with an error of less than ± 2% at 2400 °C can be merged.

Majorana-fermion origin of the planar thermal Hall effect in the Kitaev magnet α-RuCl3.

The field-induced quantum-disordered state of layered honeycomb magnet α-RuCl3 is a prime candidate for Kitaev spin liquids hosting Majorana fermions and non-Abelian anyons. Recent observations of anomalous planar thermal Hall effect demonstrate a topological edge mode, but whether it originates from Majorana fermions or bosonic magnons remains controversial. Here, we distinguish these origins from combined low-temperature measurements of high-resolution specific heat and thermal Hall conductivity with rotating magnetic fields within the honeycomb plane. A distinct closure of the low-energy bulk gap is observed for the fields in the Ru-Ru bond direction, and the gap opens rapidly when the field is tilted. Notably, this change occurs concomitantly with the sign reversal of the Hall effect. General discussions of topological bands show that this is the hallmark of an angle rotation-induced topological transition of fermions, providing conclusive evidence for the Majorana-fermion origin of the thermal Hall effect in α-RuCl3.

Implication of the double-gating mode in a hybrid photon counting detector for measurements of transient heat conduction in GaAs/AlAs superlattice structures.

Understanding and control of thermal transport in solids at the nanoscale are crucial in engineering and enhance the properties of a new generation of optoelectronic, thermoelectric and photonic devices. In this regard, semiconductor superlattice structures provide a unique platform to study phenomena associated with phonon propagations in solids such as heat conduction. Transient X-ray diffraction can directly probe atomic motions and therefore is among the rare techniques sensitive to phonon dynamics in condensed matter. Here, optically induced transient heat conduction in GaAs/AlAs superlattice structures is studied using the EIGER2 detector. Benchmark experiments have been performed at the Austrian SAXS beamline at Elettra-Sincrotrone Trieste operated in the hybrid filling mode. This work demonstrates that drifts of experimental conditions, such as synchrotron beam fluctuations, become less essential when utilizing the EIGER2 double-gating mode which results in a faster acquisition of high-quality data and facilitates data analysis and data interpretation.

Simultaneous measurement of specific heat and thermal conductivity in pulsed magnetic fields

We report an experimental setup for simultaneously measuring specific heat and thermal conductivity in feedback-controlled pulsed magnetic fields of 50ms duration at cryogenic temperatures. A stabilized magnetic field pulse obtained by the feedback control, which dramatically improves the thermal stability of the setup and sample, is used in combination with the flash method to obtain absolute values of thermal properties up to 37.2T in the 22-16K temperature range. We describe the experimental setup and demonstrate the performance of the present method with measurements on single-crystal samples of the geometrically frustrated quantum spin-dimer system SrCu2(BO3)2. Our proof-of-principle results show excellent agreement with data taken using a standard steady-state method, confirming the validity and convenience of the present approach.

Thermal Transport in 2D Materials.

In recent decades, two-dimensional materials (2D) such as graphene, black and blue phosphorenes, transition metal dichalcogenides (e.g., WS2 and MoS2), and h-BN have received illustrious consideration due to their promising properties. Increasingly, nanomaterial thermal properties have become a topic of research. Since nanodevices have to constantly be further miniaturized, thermal dissipation at the nanoscale has become one of the key issues in the nanotechnology field. Different techniques have been developed to measure the thermal conductivity of nanomaterials. A brief review of 2D material developments, thermal conductivity concepts, simulation methods, and recent research in heat conduction measurements is presented. Finally, recent research progress is summarized in this article.

Temperature Dependence of Raman Peak Shift in Single-Crystalline Si-Rich Sige

Background and Objectives Silicon-germanium (SiGe) is used for thermoelectric devices since its thermal conductivity is lower than either pure Si or Ge. Indeed, the material was used in components of the Voyager and New Horizons deep-space craft because of its superior nanoscale heat conductivity. Improving SiGe for better thermoelectric devices requires ever more precise measurements of nanoscale heat conductivity and a comprehensive study on its phonon-scattering mechanism. Especially, a relationship between Raman shift ω and temperature T (dω/dT) is required through the highly precise measurements of its temperature-dependence. Burke et al. have reported the Ge fraction dependence of dω/dT for Si-Si, Si-Ge, and Ge-Ge vibration modes of polycrystalline bulk SiGe samples with high laser power excitation [1]. However, the reported values of dω/dT may be affected by phonon scattering at grain boundaries and the local heating caused by high laser power excitation. Here, we investigated dω/dT of single-crystalline bulk SiGe and its dependence on the Ge fraction by using variable-temperature Raman spectroscopy. Experiments The (001)-oriented single-crystalline Si-rich SiGe bulk samples were prepared by two different growth methods; the Czochralski (Ge fraction: 16%) [2] and traveling liquidus zone (TLZ) methods (Ge fraction: 32 and 45%) [3]. All samples were confirmed to be strain-free by X-ray diffraction (XRD). We also measured Raman spectrum of single-crystalline Si as a reference. For Raman spectroscopy measurements, the wavelength of the excitation source was 532 nm, the focal length of the spectrometer was 2,000 mm, the laser power at the sample surface was kept to less than 1 mW. The sample temperatures were set between 50 and 300°C in 50°C steps, and the Raman signal was measured twice at each temperature (i.e., during heating and cooling). Results and Discussion Raman spectra of Si-Si mode in SiGe (Ge fraction: 16%) are shown in Fig. 1(a). With increasing temperature, the full width at half maximum (FWHM) of the Raman spectra increased and shifted toward the lower side of wavenumber. This wavenumber shift is considered to be caused by the anharmonic vibrations becoming dominant as the temperature increases, and the phonon frequency decrease due to the thermal expansion of the crystal. Figure 1(b) shows the temperature dependences of the Si-Si Raman peak shifts. We experimentally clarified the dω/dT are approximately constant in each bulk SiGe sample, as shown in Fig. 1(b). Figure 1(c) shows the Ge fraction dependence of -(dω/dT) for Si-Si mode. As a result, we found that dω/dT for Si-Si mode is independent of Ge fraction unlike the study of Burke et al. It was reported that the dω/dT depends on the coefficient of linear thermal expansion and anharmonic constants [4]. From the obtained dω/dT values in the investigated range of Ge fraction, we consider that the anharmonic constants of SiGe alloy do not change by Ge fraction. Thus, the Si-Si anharmonic vibration is supposed to be not affected by the Ge fraction in SiGe alloy. In conclusion, we determined dω/dT= -0.023 cm-1/℃ for Si-Si mode from experiments with single-crystalline bulk SiGe samples and low laser power excitation. Acknowledgement This work was supported by Grant-in-Aid for Scientific Research (21K14201).

Phase relations, structure, properties and DFT study of compounds in the Sc-rich part of the systems Sc-{Mn,Fe,Co,Ni}-Ga

Phase relations, structure, properties and DFT study of compounds in the Sc-rich part of the systems Sc-{Mn,Fe,Co,Ni}-Ga

Enhancement of charge-neutral fermionic excitations near the spin-flop transition in the magnetic Kondo material YbIr3Si7

The new Kondo material YbIr$_3$Si$_7$, similar to other Kondo insulators, has been reported to exhibit charge-neutral fermionic excitations through measurements of specific heat and thermal conductivity at low temperatures. We performed $^{29}$Si-NMR on YbIr$_3$Si$_7$ to investigate the magnetic response of charge-neutral fermions from a microscopic perspective. In low magnetic fields parallel to the $c$ axis, a single NMR peak in the paramagnetic state splits into three peaks below $T_{\rm N}$. In contrast, only a slight shift of the single NMR peak was observed in high magnetic fields. This spectral change as a function of the $c$-axis magnetic field is interpreted as spin-flop transition, at which the magnetic moments oriented along the $c$ axis (AF-I phase) are rotated to the $ab$ plane with ferromagnetic component along the $c$-axis (AF-II phase). In the vicinity of the spin-flop magnetic field $H_{\rm M}$, nuclear spin-lattice relaxation rate $1/T_1$ was found to be proportional to temperature at low temperatures, indicating the existence of charge-neutral fermions. Furthermore, a peak of $1/T_1$ vs. the $c$-axis magnetic field suggests that the charge-neutral fermions in YbIr$_3$Si$_7$ are closely related to its magnetic properties. Our findings shed light on the origin of charge-neutral fermions in insulators.

Single crystal growth of Ba2Ni(PO4)2 by using the optical floating-zone method

We report a study on the crystal growth of a frustrated antiferromagnet Ba2Ni(PO4)2 by means of optical floating-zone method. Single crystals of Ba2Ni(PO4)2 were obtained by different growth conditions. It is found that the best crystallization was obtained in pure Ar atmosphere under normal pressure and using slow growth speed of 0.6 mm/h. The X-ray diffraction data and Laue diffraction patterns demonstrate the good crystallinity of the crystals. The physical properties were characterized by magnetic susceptibility, magnetization, specific heat and thermal conductivity measurements.

Effective thermal conductivity of packed beds made of cubical particles

This work addresses the parameterization of the Zehner-Bauer-Schlünder model (ZBS), a standard model for the determination of the effective thermal conductivity of packed beds, based on thermal simulations in ANSYS. Data are presented for the effective thermal conductivity of packed beds of cubical particles, obtained from simulations of heat conduction in particle systems generated by rigid body dynamics using the open-source software Blender. The particle-to-gas thermal conductivity ratio is varied over many orders of magnitude in these simulations. Punctual validation is provided by heat conduction measurements with cubes made of plastic and aluminum in air. Structural results are validated by micro-computed X-ray tomography. Emphasis is set on bed porosity and on the relative interparticle contact area. Comparisons elucidate ZBS behavior at the limit of non-conducting particles. In the region of medium particle-to-fluid conductance, ZBS shape factor is for the first time evaluated for cubes. At high solid conductance, the effective thermal conductivity of the bed is dominated by areal contacts between particles. Such contacts are large with cubes, but they are also shown not to be thermally perfect. Contact imperfection limits the increase in bed conductivity with increasing particle conductivity and requires the introduction of an additional empirical parameter in the ZBS model. In total, a full parametric setting of ZBS is provided for cubical particles. Several sets of this kind would help to generalize the model for applicability to particles of arbitrary shape.

Anomalous heat transfer near the martensite-austenite phase transition in Ni50Mn28Ga22-x(Cu, Zn)x (x = 0; 1.5) alloys

The paper presents a detailed investigation of the thermal transport of the Ni50Mn28Ga22-x(Cu, Zn)x (x = 0; 1.5) alloys through specific heat, thermal diffusivity and thermal conductivity measurements. It is shown that the partial replacement of Ga atoms by Zn or Cu atoms leads to a convergence of magnetic and martensitic phase transition temperatures. Our measurements of the thermal diffusivity and thermal conductivity revealed that the behavior of these parameters in the phase transitions region is anomalous due to the coexistence of martensite-austenite phases and the effect of the latent heat of the phase transition. Moreover, the latent heat plays a crucial role in the appearance of a deep minimum of thermal diffusivity in the region of martensitic transformation for the Cu- and Zn-doped samples. Estimates of the phonon mean free path lph in martensitic and austenitic phase gave values of lph,mart = 1.5 nm and lph,aust = 1.9 nm, respectively. This implies that the main mechanism of phonon scattering is local structural inhomogeneities, which decrease sharply upon transition from martensite phase to the highly symmetric austenitic phase.

The Transport Properties of Quasi–One-Dimensional Ba3Co2O6(CO3)0.7

We have performed combined elastic neutron diffuse, electrical transport, specific heat, and thermal conductivity measurements on the quasi–one-dimensional Ba3Co2O6(CO3)0.7 single crystal to characterize its transport properties. A modulated superstructure of polyatomic CO32− is formed, which not only interferes the electronic properties of this compound, but also reduces the thermal conductivity along the c-axis. Furthermore, a large magnetic entropy is observed to be contributed to the heat conduction. Our investigations reveal the influence of both structural and magnetic effects on its transport properties and suggest a theoretical improvement on the thermoelectric materials by building up superlattice with conducting ionic group.

Quantum spin state transitions in the spin-1 equilateral triangular lattice antiferromagnet Na2BaNi(PO4)2

We have grown single crystals of Na$_2$BaNi(PO$_4$)$_2$, a new spin-1 equilateral triangular lattice antiferromagnet (ETLAF), and performed magnetic susceptibility, specific heat and thermal conductivity measurements at ultralow temperatures. The main results are (i) at zero magnetic field, Na$_2$BaNi(PO$_4$)$_2$ exhibits a magnetic ordering at 430 mK with a weak ferromagnetic moment along the $c$ axis. This suggests a canted 120$^\circ$ spin structure, which is in a plane including the crystallographic $c$ axis due to the existence of an easy-axis anisotropy and ferromagnetically stacked along the $c$ axis; (ii) with increasing field along the $c$ axis, a 1/3 magnetization plateau is observed which means the canted 120$^\circ$ spin structure is transformed to a up up down (UUD) spin structure. With even higher fields, the UUD phase further evolves to possible V and V' phases; (iii) with increasing field along the $a$ axis, the canted 120$^\circ$ spin structure is possibly transformed to a umbrella phase and a V phase. Therefore, Na$_2$BaNi(PO$_4$)$_2$ is a rare example of spin-1 ETLAF with single crystalline form to exhibit easy-axis spin anisotropy and series of quantum spin state transitions.

The measurement of anisotropic thermal transport using time-resolved magneto-optical Kerr effect

Owing to the increasing demand for the improved management of thermal transport in devices, it is necessary to develop an optimal method for the measurement of anisotropic heat conduction. Although several techniques have been used to measure the heat transport in anisotropic materials, the accurate determination of anisotropic thermal conductivity remains a major challenge. In this study, we present time-resolved magneto-optical Kerr effect measurement using a pump–probe technique to investigate the thermal characterization of various materials. A substrate/ferromagnetic metal (FM) structure is prepared, where FM acts as a transducer to detect the thermal transport in substrates of silicon, sapphire, and highly ordered pyrolytic graphite. By performing experiments under various modulation frequencies and laser spot sizes, we determine both in-plane and through-plane thermal conductivities. We also discuss the limitations of measurement and provide useful guidelines to determine the thermal properties of different materials with high accuracy.

FBG-Based Measurement Systems for Density, Specific Heat Capacity and Thermal Conductivity Assessment for Liquids

This paper presents the development of a thermal measurement system for density, specific heat capacity and thermal conductivity in fluids. Due to toxic and flammable environment often found in oil industry, Fiber Bragg Gratings (FBGs) were used in the sensor development, which consists in a diaphragm-embedded FBG, to estimate density, and a FBG temperature sensor, to estimate specific heat and thermal conductivity. The diaphragm system, with sensitivity of 0.025 nm/kPa, was employed for density measurements in water, diesel and crude oil, becoming a feasible option for density estimation in fluids. The temperature sensor, with sensitivity of 11.5 pm/°C, was used to propose a method to estimate specific heat and thermal conductivity. The method uses the quantity of heat equation to estimate specific heat, then, density and specific heat to estimate thermal conductivity. To validate the method, it was presented three setups based in an acrylic tank, a Becker and a test tube. The tests were performed with water, mineral oil and kryo 51 oil. In addition the proposed system can be integrated in order to realize simultaneous measurements of density, specific heat and thermal conductivity with the same structure.

Absence of long-range order in an XY pyrochlore antiferromagnet Er2AlSbO7

Rare-earth pyrochlores are known to exhibit exotic magnetic phenomena. We report a study of crystal growth and characterizations of a new rare-earth compound Er$_2$AlSbO$_7$, in which Al$^{3+}$ and Sb$^{5+}$ ions share the same positions with a random distribution. The magnetism are studied by magnetic susceptibility, specific heat and thermal conductivity measurements at low temperatures down to several tens of milli-kelvin. Different from the other reported Er-based pyrochlores exhibiting distinct magnetically ordered states, a spin-freezing transition is detected in Er$_2$AlSbO$_7$ below 0.37 K, which is primarily ascribed to the inherent structural disorder. A cluster spin-glass state is proposed in view of the frequency dependence of the peak position in the ac susceptibility. In addition, the temperature and field dependence of thermal conductivity indicates rather strong spin fluctuations which is probably due to the phase competition.

Heat conductivity of pyrolytic graphite of mark UPV-1 at temperatures 1900–2950 K

The urgency of the work is caused by that at research of heat conductivity in anisotropic materials is necessary to consider infringement of parallelism between vectors of heat flux and a gradient of temperature. In the previous works at studying heat conductivity of pyrolytic graphites techniques which were applied to isotropic graphites were used. Results of measurement of heat conductivity of pyrolytic graphite of mark UPV-1 in a direction in parallel to a plane of sedimentation are presented. The experimental samples which are heated up by an electric current, represented hollow cylinders at which the plane of sedimentation of pyrolytic graphite has been located along radius. It is offered also heat flux which defined on energy of radiation from an external surface of the sample, and a gradient of temperature to measure along radius, that is strictly in parallel each other. The comparative analysis of experimental data of heat conductivity (in parallel a plane of sedimentation), measured in the given work and resulted in literature sources is brought. The range of the investigated temperatures makes 1900–2950 K and is expanded in area of higher values on 450 K.

Absence of Magnetic Thermal Conductivity in the Quantum Spin Liquid Candidate EtMe_{3}Sb[Pd(dmit)_{2}]_{2}.

We present the ultralow-temperature specific heat and thermal conductivity measurements on single crystals of triangular-lattice compound EtMe_{3}Sb[Pd(dmit)_{2}]_{2}, which has long been considered as a gapless quantum spin liquid candidate. In specific heat measurements, a finite linear term is observed, consistent with the previous work [S. Yamashita etal., Nat. Commun. 2, 275 (2011)NCAOBW2041-172310.1038/ncomms1274]. However, we do not observe a finite residual linear term in the thermal conductivity measurements, and the thermal conductivity does not change in a magnetic field of 6T. These results are in sharp contrast to previous thermal conductivity measurements on EtMe_{3}Sb[Pd(dmit)_{2}]_{2} [M. Yamashita etal., Science 328, 1246 (2010)SCIEAS0036-807510.1126/science.1188200], in which a huge residual linear term was observed and attributed to highly mobile gapless excitations, likely the spinons of a quantum spin liquid. In this context, the true ground state of EtMe_{3}Sb[Pd(dmit)_{2}]_{2} has to be reconsidered.

Cross-plane thermal transport measurements across CVD grown few layer graphene films on a silicon substrate

Room-temperature time-domain thermoreflectance technique (TDTR) measurements of cross-plane heat conduction across gold-graphene-silicon interfaces are presented. The graphene layers are originally grown on a copper substrate by chemical vapor deposition and later transferred to a silicon substrate in layer-by-layer fashion. We estimate the thermal boundary conductance (TBC) as a function of number of graphene layers, by fitting a layered heat conduction model that accounts for heat accumulation in the gold layer to the TDTR data, using the TBC as a free fitting parameter. The estimated TBC was found to decrease with number of graphene layers at the interface, as observed in previous TDTR measurements reported in the literature. The decrease in TBC with number of graphene layers matches the trends in the transmission coefficient of low frequency (25 GHz) coherent acoustic phonons across the interface, indicating that the interface elastic stiffness decreases with the number of graphene layers due to poor bonding between the gold film and silicon substrate.

Design to Validation of a New Heat Flux Source with Uncertainty Analysis

High-speed, transient aerothermal studies produce excessive temperatures and heat fluxes in laboratory, ground, and flight-test experiments. Experiments are performed for 1) understanding the response of test vehicles under various induced thermal environments, 2) verifying computational codes and input parameters, and 3) evaluating thermophysical and mechanical characteristics of new materials. In addition to these rationales, the reconstruction of the surface heat flux from in-depth or backside instrumentation is an important inverse application. Recent research has led to an alternative view of inverse heat conduction based on calibration principles performed in the frequency domain leading to a novel “parameter-free” inverse heat conduction measurement equation. The final mathematical framework reveals that the resolution of a first-kind Volterra integral equation for the surface heat flux prediction contains only experimental data sets. This type of mathematical formulation is highly ill posed. This paper focuses on the design, fabrication, and preliminary test campaign of a new electrical heating cell for producing a verifiable heat flux source. The feasibility investigation demonstrates the merits of system through modeling, experimental design, and transient uncertainty propagation. Validation studies are presented, leading to favorable outcomes. Slug calorimetry, composed of a pure copper, is used in the validation campaign.