Specific heat measurements

Specific heat measurements [1] of " He layers on Fe203 have shown the dependency of the onset of superfluidity on the width of the film thickness. 

Nuclear magnetic resonance spectroscopy of the solutes in clathrates and low temperature specific heat measurements are thought to be particularly promising methods for providing more detailed information on the rotational freedom of the solute molecules and their interaction with the host lattice. The absence of electron paramagnetic resonance of the oxygen molecule in a hydroquinone clathrate has already been explained on the basis of weak orientational effects by Meyer, O Brien, and van Vleck.18... 

By means of the experimental methods briefly referred to in 9 a large number of specific-heat measurements have been made at very low temperatures. In Fig. 91 we haye the atomic heats of some metals, and of the diamond, represented as functions of the temperature. The peculiar shape of the curves will. be at once apparent. At a more or less low temperature, the atomic heat decreases with extraordinary rapidity, then apparently approaches tangentially the value zero in the vicinity of T = 0. The thin curves represent the atomic heats calculated from the equation ... 

The expression in Eq. (29) can be evaluated numerically for all values of t, and the results for three different waiting times are shown in Fig. 11 for c = 0.1. The value of Tmin = 2.0 ps at E/To = 5.7 x lO", derived from the present theory (also consistent with Goubau and Tait [101]) was used. The results for t = 10 ps demonstrate that, due to a lack of fast relaxing systems at low energies, short-time specific heat measurements can exhibit an apparent gap in the TLS spectrum. Otherwise, it is evident that the power-law asymptotics from Eq. (30) describes well Eq. (29) at the temperatures of a typical experiment. 

We wish to note that 0D can also be calculated from the measured ultrasonic velocities, and data should be equal to those obtained from specific heat measurements. The Debye s temperature evaluated from data of ultrasonic velocity is (see e.g. [14,15]) ... 

Fig. 3.9. Specific heat of FeCl2 4H20 drawn from data obtained by Friedberg et al. [35] and Raquet and Friedberg [36]. The peak near 1K is only partly shown, the highest value of the specific heat measured being... 

A gold film (thickness 0.1 xm, and residual resistance R 911) was deposited onto the crystal in order to obtain a heater of negligible heat capacity. It was carefully checked that the film resistance was constant along the temperature range of the specific heat measurements. 

Fig. 12.6. View of the experimental assembly for specific heat measurement of the Te02 crystal. The electrical connections of the gold film heater (left) and of the NTD Ge thermistor (right) are also shown.

The band electronic structure of kl-(BEDT-TTF)2Cu(CF3)4(TCE) was calculated through the use of Hiickel tight binding computations [39] and the infrared properties analyzed [40]. These calculations indicate that the electronic band structure [10, 41] and infrared response [42] is similar to that found in the k-(BEDT-TTF)2Cu(dca)X (X = Cl and Br) salts. Specific heat measurements of kl-(BEDT-TTF)2Ag(CF3)4(TCE) indicate a linear coefficient (y = 50 mJ mol 1 K2), which is a factor of nine greater than expected from a free-electron picture [43],... 

Specific heat measurements on Ba02 were carried out by DTA for conversion of this value to 25 °C... 

Johannson (1937) is generally credited with the earliest calculations of Gb C f c.c. which were based on the specific heat measurements of Austin (1932). 

Controversial discussions ensued concerning the magiutude of the gap of the spin liquid state. Specific heat measurements suggested a gapless nature [358], while thermal conductivity measurements suggested a small gap [359]. Furthermore, there is an abnormality in lattice near 5-6 K which was detected by NMR [357] and thermal expansion [360] measurements, indicating that the lattice is not frozen even at 5-6 K. 

The Stoner product (30), calculated across the actinide series for homologous compounds, may interpret (or predict) the magnetic behaviour of these solids, and hence suggest a localized or itinerant picture (see Chap. D), provided that we know I for the different actinides across the series, since N(pf) is measurable (e.g. through specific heat measurements) and roughly reciprocal to the bandwidth W (N(pf) W ). I is not directly measurable and must be calculated. (Of course, the discussion above shows that the two quantities are not really independent, since the interactions determining I also play a role in determining the bandwidth, and hence N([Xf).)... 

Scientific awareness of a low-temperature transition in magnetite began in 1929 with the observation of a A-type anomaly in the specific heat at about 120 K. The anomaly was typical of an order-disorder transition, but it was well below the magnetic-ordering temperature Tc = 850 In 1931, Okamura observed an abrupt semiconductor-semiconductor transition near 120 K. The transition exhibits no thermal hysteresis, but the transition temperature is sensitive to the oxygen stoichiometry. More recent specific-heat measurements show the presence of two resolvable specific-heat peaks at the transition temperature the lower-temperature peak near 110 K appears to be due to a spin reorientation. 

Based on ac magnetic susceptibility and specific heat measurements, El Massalami et al. (1998a) claimed that they observed superconductivity in CeNi2B2C with Tc of about 0.1 K. If this will be confirmed the mechanisms for superconductivity in the whole borocarbide series should be reconsidered. 

Fig. 60. Concentration dependence of various properties of polycrystalline Y(Ni xPt )2B2C obtained by specific heat measurements transition temperature Tc exponent a and parameter Hc2 from eq. (6) upper critical field Hc2(0) at T =0, where the dotted line schematically describes the dirty limit corresponding to the isotropic single band case (in reality there is a finite intersection with the field-axis for the dotted asymptotic line, see Shulga and Drechsler 2002) exponent fi of eq. (8) for the curvature of the electronic specific heat in the mixed state and Sommerfeld constant xn (after Lipp et al. 2001).

From a specific heat measurement, the approximate atomic weight of a metal (M) is found to be 133 A 0 2341 g sample of M is heated to constant weight in air to convert it to the oxide The weight of the residue is 0 274s g Find the true atomic weight of the metal (and therefore its identity), and determine the formula of the metal oxide... 

Before the advent of ultraviolet photoelectron spectroscopy and ESCA, experimental evidence on the energy density was mainly available from static magnetic susceptibility and specific heat measurements (134). These provide information on the density of states at the Fermi level and it is impossible to base any conclusions on such experimental information with regard to the shapes of the d-bands in the alloys. It is currently believed that there is very little transfer of d-electrons between the atoms. If an increase in the number of d-electrons on a particular atom does occur, it is due to transfer of electrons from the s,p-band to the lower d-band. This is, of course, related to the difference in electronegativity of the alloying components (135a, 135b). 

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