Specific Heat Of Cu Research Articles

Specific heat of Cu substituted GdNiSi

The specific heat of magnetic regenerator materials affects the efficiency of cryocoolers below 10 K. GdNiSi with the orthorhombic TiNiSi-type structure shows antiferromagnetic order at 11 K. To tune the magnetic transition temperature below 10 K, Cu substituted GdNiSi alloys were prepared. Powder X-ray diffraction and specific heat measurements were performed to study the effect of Cu substitution on the crystal structure and magnetic transition temperature. Increasing Cu content, the secondary phase which may be the hexagonal BeZrSi-type GdNi1−x Cu x Si is observed. The peak of the specific heat for x ≤ 0.2 was shifted higher temperature (13 K) due to the magnetic transition, though the unit cell volume of the TiNiSi-type structure slightly increased with increasing x. This result possibly originates from the increase of the RKKY interaction for the sinusoidal curve due to an increase of the intersite distance of Gd-ions.

High-pressure phonon dispersion of copper by using the modified analytic embedded atom method

By using the Born—von Kármán theory of lattice dynamics and the modified analytic embedded atom method, we reproduce the experimental results of the phonon dispersion in fcc metal Cu at zero pressure along three high symmetry directions and four off-symmetry directions, and then simulate the phonon dispersion curves of Cu at high pressures of 50, 100, and 150 GPa. The results show that the shapes of dispersion curves at high pressures are very similar to that at zero pressure. All the vibration frequencies of Cu in all vibration branches at high pressures are larger than the results at zero pressure, and increase correspondingly as pressure reaches 50, 100, and 150 GPa sequentially. Moreover, on the basis of phonon dispersion, we calculate the values of specific heat of Cu at different pressures. The prediction of thermodynamic quantities lays a significant foundation for guiding and judging experiments of thermodynamic properties of solids under high pressures.

A new heat capacity measurement scheme based on the scanning relaxation method for the Si–N membrane microcalorimeter at high temperatures up to 700 K

We present a sensitive heat capacity measurement method for use at temperatures between 300 and 700 K using a home-made calorimeter incorporating a Si–N membrane microcalorimeter and a commercial tube furnace. We employ a scanning relaxation method with the two relaxation times, in which temperature is scanned with a maximum speed up to ∼30 K/min to measure the heat capacity of sub-mg single crystals. The heat capacity of the addenda composed of the Si–N membrane and thermal grease is measured to be as small as ∼30 μJ/K. For the high temperature thermal grease, several materials such as In, Wood's metal, and silicone oil have been tested. We demonstrate the successful performance of this method with different scanning speeds by measuring the specific heat of Cu up to 620 K. A brief summary of advantages/disadvantages of this method vis-à-vis commercially available differential scanning calorimeters (DSCs) is given.

The specific heat of Cu–Al–Ni shape memory alloys

The specific heat of Cu 81.8Al 13.7Ni 4.5 (AK10) shape memory alloy has been studied by means of conventional DSC and adiabatic calorimetry techniques. The transformation temperatures and the shape of the calorimetric curves obtained by adiabatic calorimetry do not show any noticeable dependence on the temperature measurement rates, contrarily to what is observed by other calorimetric techniques. The dynamical character of the various experimental methods together with the influence of the latent heat associated to the first order character of these phase transitions are discussed. The specific heat of AK10 has been measured from 50 to 350 K which covers the phase transformation temperature range. The forward and reverse martensitic transformation peaks were found at 299.5 and 304.6 K, showing a thermal hysteresis of 5.1 °C. The C p accuracy can be estimated in 0.1% of C p and permits a reliable assignment of the following values to the phase transition thermodynamic functions: Δ H = 7.4 ± 0.2 J/g and Δ S = 0.025 ± 0.001 J/gK.

Magnetic specific heat analysis of Cu(C 2H 8N 2) 2Ni(CN) 4: A quasi-two-dimensional heisenberg antiferromagnet

The specific heat of Cu(C 2H 8N 2)Ni(CN) 4 measured in the temperature range from 80 mK to 2 K revealed significant deviations from the assumed one-dimensional (1D) magnetic behaviour. The behaviour of short range correlations was described by a S= 1 2 quadratic Heisenberg antiferromagnetic model with the exchange constant J k =−180 mk . Intrachain covalent bonds are completed by bifurcated hydrogen bonds of the NH…N(C)…HN type connecting adjacent chains and creating a 2D net of exchange paths. The origin of the λ-like anomaly in the specific heat observed at 128 ± 2 mk was ascribed to the 2D–3D crossover in magnetic lattice dimensionality activated by the interlayer dipolar interaction.

Corrections to scaling in the specific heat of Cu(NH4)2Br4·2H2O near Tc

The specific heat of the Heisenberg ferromagnet Cu(NH 4 ) 2 Br 4 ·2H 2 O has been measured with high resolution near T c . The data outside the ‘rounded’ region are consistent with power law behavior including first order corrections to scaling: C R = ( A α )t −α (1 + Dt x ) + B . The fitted parameters agree well with predictions for a 3-dim Heisenberg model with short range interactions.

Susceptibility and Specific Heat for Cu(NH3)2·Ni(CN)4·2C6H6

The magnetic susceptibility and the specific heat of Cu(NH 3 ) 2 ·Ni(CN) 4 ·2C 6 H 6 in powder specimen has been measured between 0.2 and 20.4 K. Broad maximums are observed near 3 K in both experimental results, but the information for phase transition to the long range order can not be obtained down to 0.2 K. These results give the behaviour of low dimensional magnetic lattice for this crystal. The susceptibility data is explained as the one dimensional antiferromagnetic spin system with exchange interaction | J |=2.31 K.

Calorimetry below 1 K: The specific heat of copper

A technique is described which permits the accurate measurement of heat capacities to very low temperatures without the use of a heat switch. As a test of this technique the specific heat of Cu, with and without hydrogen impurities, has been measured in the temperature range 0.04–1 K. The presence of hydrogen increases the specific heat by ≈ 1% as has been reported previously at higher temperatures. Above 0.3 K the data for hydrogen-free copper are in good agreement with the copper reference equation. At lower temperatures there is an additional contribution to the heat capacity which may be associated with oxygen impurities.

Crystal Dynamics and Electronic Specific Heats of Palladium and Copper

Using inelastic neutron scattering, the frequency – wave vector dispersion relations for the lattice vibrations in a single crystal of palladium have been determined at 120, 296, 673, and 853 °K. Analyses of the results have given force-constant models from which frequency distributions have been computed. First-neighbor interactions are dominant, but weaker interactions also exist, extending beyond sixth-nearest neighbors. The total lattice specific heat (harmonic plus anharmonic) at constant pressure has been calculated, using the frequency distribution at 296 °K and the shifts in the frequencies with changing temperature. Similar calculations were also carried out for copper, using the room temperature distribution reported by Svensson et al.; the temperature dependence of the frequencies was established by carrying out measurements along major symmetry directions of Cu at 296, 473, and 673 °K. The electronic specific heats of Cu and Pd have been calculated at temperatures between 0 and 900 °K. The electronic specific heat of Cu agrees well enough with the linear relation Ce = γT for T < 700 °K. For Pd, Ce is anomalously high at low temperatures, in agreement with experiments at helium temperature, but tends to saturate for temperatures > 200 °K.

Specific Heat of Dilute Solutions of Fe in Cu–Al Alloys

The specific heat of Cu–Al and Cu–Al:Fe alloys containing 0, 5, and 10 at.% Al and 0.07 at.% Fe has been measured in the temperature range 1.2° –14° K. The excess specific heat due to the Fe impurities is decreased with increasing Al concentration. The data are compared with various predictions based on the Kondo model for dilute magnetic alloys. The decrease in the excess specific heat is consistent with the corresponding decrease in the magnetic moment of the Fe with increasing Al concentration determined by high-temperature susceptibility data. A further systematic change in the temperature dependence of the excess specific heat is attributed to an increase in the Kondo parameter TK with increasing Al. The measurements strongly support the hypothesis that the excess specific heat is associated with the Kondo effect, and that interactions among impurities is not the mechanism.

Specific Heat of Cu(NH3)4(NO3)2

The specific heat of Cu${(\mathrm{N}{\mathrm{H}}_{3})}_{4}$${(\mathrm{N}{\mathrm{O}}_{3})}_{2}$ has been studied over the temperature range 1.2-16\ifmmode^\circ\else\textdegree\fi{}K. The results show a broad maximum similar to that reported in other substances that magnetically order in linear chains. By comparing with the calculations of Bonner and Fisher, it is determined that the substance forms antiferromagnetic linear chains with a nearest-neighbor Heisenberg interaction constant of $\frac{J}{k}=(3.70\ifmmode\pm\else\textpm\fi{}0.04)\ifmmode^\circ\else\textdegree\fi{}$K.

Specific heat of Cu(NH3)4SO4.H2O below 1°K

The specific heat of Cu(NH3)4SO4.H2O has been measured down to 0.03°K, by studying the rate of change of the temperature when a single crystal of the salt was cooled through a known thermal resistance. Susceptibility measurements in the directions of the three crystalline axes were performed.The results are in agreement with the idea that, as far as the magnetic interactions are concerned, the copper ions are arranged in linear chains. The specific heat shows a broad Schottky type maximum near 3°K and a small sharp maximum at 0.37°K which may correspond to the appearance of long range magnetic order. The susceptibility measurements are in general agreement with this picture. A value of J/k = −7°K is derived for the exchange constant in a chain, from the susceptibility as well as from the specific heat data.

On the influence of nuclear spin and of super-exchange on the spin specific heat of cu(nh 4) 2(so 4) 2.6h 2o

Synopsis It is wellknown that the specific heat of the spin system of most cupric salts is much higher than can be explained by magnetic interaction alone. This is generally thought to be due to super-exchange interaction. Since the Cu-nuclei carry a magnetic moment it has to be expected that interaction with the electronic spin of the ion will cause a small splitting, which will also contribute to the specific heat of the spin system. The magnitude of this effect has been determined in the case of Cu(NH 4 ) 2 (SO 4 .6H 2 O by comparing paramagnetic relaxation measurements on this salt with results obtained with a magnetically diluted isomorphous double-salt (5% Cu ++ , 95%Mg + + ).