56 research outputs found
Heat capacity and phonon mean free path of wurtzite GaN
We report on lattice specific heat of bulk hexagonal GaN measured by the heat
flow method in the temperature range 20-300 K and by the adiabatic method in
the range 5-70 K. We fit the experimental data using two temperatures model.
The best fit with the accuracy of 3 % was obtained for the temperature
independent Debye's temperature {\rm K} and Einstein's
temperature {\rm K}. We relate these temperatures to the
function of density of states. Using our results for heat conduction
coefficient, we established in temperature range 10-100 K the explicit
dependence of the phonon mean free path on temperature . Above 100 K, there is the evidence of contribution of the Umklapp
processes which limit phonon free path at high temepratures. For phonons with
energy {\rm K} the mean free path is of the order 100
{\rm nm}Comment: 5 pages, 4 figure
Перша міжнародна науково-практична конференція «Комп'ютерне моделювання в хімії та технологіях»
The influence of the disordered dipole subsystem on the thermal conductivity of the CO solid at low temperatures
The thermal conductivity of solid CO was investigated in the temperature range 1–20 K. The experimental temperature dependence of thermal conductivity of solid CO was described using the time-relaxation method within the Debye model. The comparison of the experimental temperature dependences of the thermal conductivity of N₂ and CO shows that in the case of CO there is an additional large phonon scattering at temperatures near the maximum. The analysis of the experimental data indicates that this scattering is caused by the frozen disordered dipole subsystem similar to a dipole glass. The scattering is described by the resonant phonon scattering on tunnelling states and on low-energy quasi-harmonic oscillations within the soft potential model
Heat transfer in Ar and N₂ doped solid CO
The measurements of thermal conductivity coefficient of a solid carbon monoxide crystal containing argon
and nitrogen admixtures at different concentrations (1.5, 3, 6, 12.5, 25% for N2 and 0.5, 1, 1.25, 2, 4% for Ar)
were performed in the temperature range from 1.5 to 40 K by steady-state heat flow method. For analysis of the
experimental data the Callaway method in the framework of the Debye model was used. The contribution of various
mechanisms of phonon scattering, including scattering by disordered dipoles of the CO matrix, to the thermal
conductivity of CO–N₂ and CO–Ar solid solutions were taken into account
The peculiarities of heat transfer in CO₂ and N₂O solids at low temperatures
The thermal conductivities of CO₂ and N₂O solids have been investigated in the low-temperature range
1–40 K. The thermal conductivities of CO₂ and N₂O are large compared with those of simple molecular crystals
such as N₂, CO, or O₂ in the whole investigated temperature range. Analysis of the experimental data by
the Callaway method shows that relatively large size of crystalline grains, low density of dislocations and
weak phonon–phonon interaction might be the reasons for the good thermal conduction in these crystals at
temperatures near the maxima. A comparison between calculated values of the intensity of normal phonon
scattering processes and experiment gives evidence that in N₂O there is an additional (in comparison with
CO₂) giant scattering of phonons. This scattering is described in the frameworks of soft potential model by
the resonance phonon scattering on tunnel states and low-energy vibratons
Influence of thermal treatment on thermal properties of adamantane derivatives
Heat transport mechanisms present in 2-adamantanone and 1-cyanoadamantane crystals were investigated
in a broad temperature range. To characterize scattering processes, thermal conductivity and heat capacity measurements
were carried out. A particular care was paid to the cooling rate of specimen which influenced the thermal
history of the samples. The experimental results led to a conclusion that under slow cooling the thermal conductivity
reaches the highest values and resembles the behavior of ordered molecular crystals. As for fast
cooling, the “quenching” resulted in changes in both the structure and the temperature dependence of the thermal
conductivity, the latter resembling that of amorphous solids. In heat capacity measurements the thermal history
made on samples did not reflect the preliminary findings known from thermal conductivity results, which could
imply that the observed mechanisms are more complex
Thermal conductivity of argon–SiO₂ cryocrystal nanocomposite
The effective thermal conductivity of samples of cryocrystal nanocomposite obtained from argon and SiO2
nanopowder was determined in the temperature interval 2–35 K using the steady-state method. The thermal conductivity
of crystalline argon with nanoparticles of amorphous silica oxide embedded in its structure shows a weak dependence
on particle linear dimension in the interval 5–42 nm. The temperature dependence of the thermal conductivity
of the nanocomposites can be well approximated by taking into account only the two mechanisms of heat
carrier scattering: phonon-phonon interaction in U-processes and scattering of phonons by dislocations
Excess thermal resistivity in N₂–CO solid solution at low carbon monoxide concentration
The results of measurements of the thermal conductivity of pure and carbon-monoxide-doped nitrogen crystals, for samples containing up to 0.7% of CO molecules, in the temperature range 1.2–26 K are presented. From the preliminary analysis it results that the interaction of phonons with admixture molecule featuring the same mass, as the host molecule, is relatively weak and depends weakly on the admixture concentration within investigated range of carbon monoxide in nitrogen crystal
Investigations of thermal conductivity of simple van der Waals crystal-based nanocomposites
The experimental setup for obtaining and determination of the thermal conductivity of simple van der Waals
crystal-based nanocomposites is described. Preliminary thermal conductivity results of measurements carried out
in the temperature range 1–40 K on two samples of methane crystals containing nanoparticles of hydroxyapatite
are presented. These results confirm usability of the setup and its suitability as a proper experimental method for
investigations of the thermal conductivity of the nanocomposites
Thermal conductivity of donor-doped GaN measured with 3ω and stationary methods
The thermal conductivity of three single crystal samples of n-type gallium nitride with electron densities of
4.0⋅10¹⁶, 2.6⋅10¹⁸, and 1.1⋅10²⁰ cm⁻³ has been determined in the temperature range 4–320 K. The measurements
were carried out within the ab plane using the stationary method. The thermal conductivity depends strongly on
the donor concentration. The analysis within the Callaway approach and the Debye model shows a significant influence
of phonon–electron scattering on the thermal conductivity of the samples. In addition, some preliminary
results obtained along the c axes of GaN layered samples are presented. The latter measurements have been carried
out using the 3ω method
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