Papers by Piotr Stachowiak
Journal of the European Ceramic Society
Superconductor Science and Technology
International Journal of Modern Physics B
Results of NMR studies of the nuclear spin-spin relaxation times at low temperatures are reported... more Results of NMR studies of the nuclear spin-spin relaxation times at low temperatures are reported for commensurate monolayers of 3 He physisorbed on hexagonal boron nitride. Temperature independent relaxation rates are observed for 0.11< T <0.56 K, and are interpreted in terms of the quantum exchange motions of the 3 He atoms. The relaxation times and the inferred effective exchange rates were observed to change significantly on replacing the 3 He atoms with relatively immobile Ne atoms. This result is understood in terms of a large 3-spin exchange in addition to 2-spin exchange.
Journal of Alloys and Compounds, 2017
Physical Review B Condensed Matter and Materials Physics, 2007
A hysteresis of the thermal conductivity of (CD4)1-c(CH4)c solid solutions has been detected in t... more A hysteresis of the thermal conductivity of (CD4)1-c(CH4)c solid solutions has been detected in the vicinity of the phase transition from partially orientationally ordered phase II to completely orientationally ordered phase III. The temperature interval of the hysteresis increases with the CH4 concentration increase. An explanation is proposed, which attributes the hysteresis to the existence of a steady mixed two-phase state near the first-order phase transition. The state is observed in a wide range of temperatures.
Low Temperature Physics, 2006
The temperature dependence of the magnetic susceptibility of polycrystalline oxygen samples is me... more The temperature dependence of the magnetic susceptibility of polycrystalline oxygen samples is measured in the range from 1 to 54 K. The measurements are performed using our home-designed SQUID-based gradiometer. The sensitivity of the instrument with respect to susceptibility reaches values of the order of 10-13. The results are compared with data in the literature.
Low Temperature Physics, 2015
The thermal conductivity of three single crystal samples of n-type gallium nitride with electron ... more The thermal conductivity of three single crystal samples of n-type gallium nitride with electron densities of 4.0⋅10 16 , 2.6⋅10 18 , and 1.1⋅10 20 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.
Solid State Communications, 2014
ABSTRACT Order or disorder in subsystem of dipolar constituents of a solid often significantly in... more ABSTRACT Order or disorder in subsystem of dipolar constituents of a solid often significantly influences its physical properties. The results of investigation of the effect of glassy state in subsystem of carbon monoxide molecules on thermal conductivity of CO crystal in its equilibrium vapor pressure are reported. The thermal conductivity of a high quality carbon monoxide crystal was specified over the temperature range 1.2–45 K. The results of these measurements were analyzed within the frame of relaxation time approximation. It was shown that at low temperatures phonon scattering by subsystem of disordered CO molecules is the most significant dissipative mechanism of heat transfer in the investigated crystal.
Low Temperature Physics, 2015
The measurements of thermal conductivity coefficient of a solid carbon monoxide crystal containin... more 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 N 2 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 CON 2 and CO-Ar solid solutions were taken into account. PACS: 44.10.+i Heat conduction; 63.20-e Phonons in crystal lattice; 63.20.Mt Phonon-defect interactions; 65.40.-b Thermal properties of crystalline solids.
Physica B: Condensed Matter, 2015
ABSTRACT The low-temperature dependence of thermal conductivity coefficient of dielectric crystal... more ABSTRACT The low-temperature dependence of thermal conductivity coefficient of dielectric crystals on temperature spreads over a vast region, both in terms of the absolute value of the coefficient as well as its functional dependence on the temperature. However, we were able to notice a group of simple molecular polycrystals which show their thermal conductivity very close to each other. What is more, the similarity of the thermal conductivity of the polycrystals for many reasons resembles known and studied for over 30 years the universality observed for low-temperature thermal conductivity of amorphous solids. Here, utilizing already developed thermal conductivity models, we try to understand what phenomena could result in the similarity of the thermal conductivity of the polycrystals and therefore explain the finding. Provided that some other conditions are met at least each of three different phonon scattering mechanisms could lead to the similarity.
The results of NMR studies of the nuclear spin-spin relaxation are reported for commensurate mono... more The results of NMR studies of the nuclear spin-spin relaxation are reported for commensurate monolayers of helium three adsorbed on hexagonal boron nitride. The measurements were made using pulsed NMR techniques for low temperatures, 0.01 < T < 5.0 K, and for moderately high magnetic fields (up to 6 T). The relaxation rate is independent of temperature at low temperatures, 0.12 < T < 0.85 K, and this behavior is interpreted in terms of particle-particle exchange motions of the adsorbed helium atoms. The effective exchange rates were observed to change significantly on replacing a fraction of the helium atoms with relatively immobile neon atoms. This is understood if there is a significant 3-particle exchange in addition to 2-particle exchange. The analyses of the experimental results indicate that the 3-spin exchange term in the exchange Hamiltonian is of opposite sign to that of the 2-spin exchange and also has a larger amplitude. At high temperatures, 0.8 < T < 5...
Results are reported for pulsed NMR studies of ^3He adsorbed on hexagonal boron nitride. A 0.75 f... more Results are reported for pulsed NMR studies of ^3He adsorbed on hexagonal boron nitride. A 0.75 fraction of a monolayer, corresponding to the boundary of the commensurate and incommensurate phases of ^3He on BN, was studied. The temperature dependence of the nuclear spin-spin and spin-lattice relaxation times have been measured for the temperature range 0.1-5 K. The relaxation times are used to deduce the correlation times of the atomic motions of ^3He. From the correlation times, the quantum mechanical exchange rates are obtained for a triangular array of ^3He atoms.
Journal of Low Temperature Physics
Results are reported for high frequency pulsed NMR studies of 3 He adsorbed on hexagonal boron ni... more Results are reported for high frequency pulsed NMR studies of 3 He adsorbed on hexagonal boron nitride. The commensurate coverage, corresponding to a 0.75 fraction of a monolayer was studied. The temperature dependence of the nuclear spin-spin relaxation time was measured in the range of 0.1-2 K. From the relaxation times, the quantum mechanical exchange rates are calculated for a triangular array of 3 He atoms.
ABSTRACT Thermal conductivity of solid CO was investigated over the temperature range 1.3–37 K by... more ABSTRACT Thermal conductivity of solid CO was investigated over the temperature range 1.3–37 K by steady state flow method. The thermal conductivity coefficient reaches its maximum value 28 mW/cm K at about 6 K. Problem of the dipolar ordering at low temperatures has been discussed.
Physical Review B, 1998
ABSTRACT The measurements of thermal conductivity of solid methane with krypton impurity (concent... more ABSTRACT The measurements of thermal conductivity of solid methane with krypton impurity (concentrations of the impurity were 0.015%, 0.338%, and 1.105%) were performed in the temperature range from 1.4 K to 20 K. The analysis of the experimental data of both pure and impurity containing crystals was performed within the framework of the time-relaxation model. The temperature dependence of thermal conductivity of solid methane was described by using the following phonon-scattering processes: boundary scattering, phonon-phonon scattering (U processes), scattering by point defects, and elastic interaction with the rotational motion of methane molecules. It was shown that the elastic interaction of phonons with almost freely rotating molecules (Oh symmetry sites) is the main phonon relaxation process that determines the thermal conductivity of methane in the low-temperature phase. The value of the phonon-rotational interaction parameter in this phase was obtained. The process of resonance phonon scattering on a heavy isotope impurity was used to describe the impurity effect of Kr. The analysis showed that the temperature dependence of thermal conductivity of doped methane can be described with the assumption that the introduction of the atomic impurity of Kr deforms the rotational spectrum of methane.
High Temperatures-High Pressures, 1997
Physical Review B, 1998
ABSTRACT Thermal conductivity investigations of pure and oxygen doped argon crystals have been ca... more ABSTRACT Thermal conductivity investigations of pure and oxygen doped argon crystals have been carried out over the temperature range 1.3–26 K. Samples with oxygen concentration of 0.008, 0.024, 0.063, 0.225, and 0.390 mol % were measured. The result is that the interaction of phonons with the spin-rotational motion of oxygen molecules in an argon matrix is the most significant among possible mechanisms of phonon scattering by the impurities. In the thermal conductivity of the samples, no mutual interaction of the oxygen impurities has been observed over the investigated impurity concentration range.
Physical Review B, 2003
ABSTRACT Thermal conductivity of crystalline nitrous oxide was investigated over the temperature ... more ABSTRACT Thermal conductivity of crystalline nitrous oxide was investigated over the temperature range 1.2–40 K. Temperature dependence of the thermal conductivity has been determined at temperatures below 23 K. Thermal conductivity coefficient exhibits a surprisingly—compared with simple molecular crystals such as N2, CO, or O2—high value in the whole investigated temperature range. Both the experimental results themselves and the method of Callaway applied to the experimental data analysis indicate that relatively low density of dislocations and weak phonon-phonon interaction might be reasons for the good thermal conduction in solid N2O. The problem of influence of possible low-temperature dipolar ordering on thermal conductivity of nitrous oxide crystal is speculated.
Advances in Optical Materials, 2011
ABSTRACT Optical spectra, excited state relaxation dynamics and thermal conductivity in a wide te... more ABSTRACT Optical spectra, excited state relaxation dynamics and thermal conductivity in a wide temperature region for thulium-doped YVO4, GdVO4 and LuVO4 have been measured and analyzed to assess thermal effects in laser-diode-pumped Tm:vanadate lasers.
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Papers by Piotr Stachowiak