Low-temperature Thermal Expansion Research Articles

Thermal expansion of the disordered conductors MNiSn (M=Ti,Zr,Hf).

We report on the behavior of the low-temperature transport properties and thermal expansion of the intermetallic compounds MNiSn (M=Ti,Zr,Hf) through the metal-insulator transition. In the low-conductivity samples [\ensuremath{\sigma}\ensuremath{\sim}${10}^{2}$ (\ensuremath{\Omega} cm${)}^{\mathrm{\ensuremath{-}}1}$] situated on the metallic side, the conductivity \ensuremath{\sigma} varies at T10 K as \ensuremath{\sigma}\ensuremath{\approxeq}${\mathrm{\ensuremath{\sigma}}}_{0}$+${\mathit{A}}_{0}$ \ensuremath{\surd}T , which may be ascribed to a Coulomb-interaction correction. For the same temperature interval an anomalous negative thermal expansion with negative values approximately proportional to the degree of interaction, evaluated from the conductivity, was observed. A discussion of the possible effect of electron-electron interaction on the electron thermal expansion based on the results of Altshuler and Aronov is also presented.

Low-temperature thermal expansion of SmB6: Evidence for a single energy scale in the thermodynamics of Kondo insulators.

We have measured the thermal expansion of the Kondo insulator SmB[sub 6] from 5 to 80 K using a sensitive capacitance dilatometer. There is a pronounced negative anomaly in the linear expansion coefficient [alpha], of electronic origin, which achieves a local minimum of [minus]5[times]10[sup [minus]6] K[sup [minus]1] at 45 K. We interpret this anomaly as a Schottky-like contribution arising from transitions across a semiconducting energy gap [ital E][sub [ital g]][congruent]140 K. Although there are several energy scales in the problem, a Grueneisen analysis indicates that the thermodynamics is driven by a single energy, which we identify as the gap energy.

Hyperfine structure and properties of new invar alloy Fe [sbnd]Ni [sbnd]C at low temperatures

Hyperfine magnetic structure and low temperature thermal-expansion of alloy Fe-30.4Ni-1.5Ccomparing to binary Fe-30.6Ni and Fe-36.0Ni ones have been studied by means of Mossbauer spectroscopy. It was found that unlike the well known invar Fe-36.0Ni alloy the embedding of C to Fe-30.6Ni ones improves the invar and mechanical properties. The properties of ternary alloy were found to be depend on homogenization temperatures 800–1470K. The positive effect of C is explained to be caused by the influence on the atomic and magnetic ordering in alloys.

Low-temperature Thermal Expansion Anomalies in Indium and Its Solid Solution Alloys with Thallium

Low-temperature thermal expansion measurements have been made for fct, solid solution indium-thallium single-crystal alloys containing 6, 19, 24 and 29 at.% Tl. The expansion coefficients along the a and c axes for the 6, 19 and 24% alloys follow the same anomalous variations with temperature below about 15 K as for those of pure indium, with no change in magnitude. This contrasts with an increased magnitude for the anomalies previously reported for an In26�5at.%TI alloy and reported here for the a-axis expansion for In29at.%Tl. These observations are discussed in terms of the Fermi surface topology for indium and their implications for the fcc to fct transformation in In-TI alloys being electronically driven.

Low-temperature thermophysical properties of Fe3Si

Abstract Measurements of the thermal expansion of Fe3Si in the temperature range 2-300 K are reported. The low-temperature linear thermal expansion of Fe3Si is accurately described by the expression α = (-3·5±0·5)x 10−9 T + (47middot;07plusmn;2) × 10−12 T 3 K−1, being the sum of a linear electronic contribution and a cubic lattice contribution. The thermal expansion is negative below 24 K. The failure to find evidence for low-temperature T 3/2 spin-wave contributions to the low-temperature thermophysical properties of Fe3Si is shown to be consistent with the very low values for the spin-wave thermophysical coefficients predicted on the basis of neutron-scattering experiments. Values for the electronic and lattice Gruneisen parameters in the low-temperature limit are calculated. The negative electronic Gruneisen parameter for Fe3Si is shown to be consistent with band-structure calculations which all predict a large peak in the electronic density of states at the Fermi surface.

Temperature dependence of magnetovolume for Ni-Cr alloys near the critical composition for magnetism

Measurements of the low-temperature thermal expansion coefficient, α, of Ni-Cr alloys close to the critical concentration, x c, for the ferromagnetic regime may be represented in the form α= A+BT+CT 3. The value for A increases in magnitude as x c is approached and abruptly changes sign at x c, being positive in the paramagnetic alloys and negative in the ferromagnetic alloys. Further measurements are reported that support a qualitative description proposed to account for the sign change in A, which is based upon a correspondence between the magnetovolume and the magnitude of the ordered magnetic moment and the moment fluctuation associated with the magnetic transition.

Low-temperature thermal expansion of PEEK, HTA and some of their composites reinforced with carbon fibres

The thermal expansion of poly(ether ether ketone), a modification of poly (ether sulphone) and carbon fibre reinforced composites of these polymers has been measured over the range −153 to 27°C with a push-rod diameter. Where other measurements are available for comparison, agreement is obtained within experimental scatter. Some multidirectional composites are tested and the measured values of thermal expansion are explained qualitatively. It is thought that the specimen size has had a significant effect on these results. The longitudinal and transverse coefficients of thermal expansion of Hercules AS4 fibre have been calculated.

Magnetization experiments down to 100 mK on single crystalline heavy-fermion Ce 0.95 La 0.05 Ru 2 Si 2

The heavy-fermion system Ce 0.95 La 0.05 Ru 2 Si 2 undergoes a metamagnetic transition al B * ≈5.3 T. We have performed extensive low-temperature (0.1 K ≤ T ≤ 1.5 K) magnetization measurements using a SQUID magnetometer. We observe that for fields above and below B * (B 8T) the magnetization is proportional to T 2 . The results are compared with low-temperature (0.3 K ≤ T ≤ 2.0 K) thermal-expansion experiments in magnetic fields up to 8 T, performed on the same single crystal. A simple scaling ansatz with one unique parameter describes the magnetic field behaviour on both sides of B *.

Low temperature dilatation measurements in the silicate research

The main application fields of thermal expansion measurements in the silicate research are summarized. Special emphases is given to frost dilatometry, the expansion effect due to water freezing on the low temperature thermal expansion curves of water saturated porous solids.

Thermoelastic properties of 350 grade maraging steel

The elastic moduli of 350 grade maraging steel in the annealed and hardened states have been determined in the temperature range 4.2 to 300 K. Thermal expansion of these steels and pure iron are given for the range 2 to 800 K. The elastic moduli show a normal temperature dependence, increasing with decreasing temperature, and a zero temperature derivative at 0 K. The low-temperature thermal expansion coefficient is the sum of a linear and cubic term, the former having a negative sign for the steels, which is probably due to magnetic effects. The elastic moduli increase by about 10% on hardening, and this increase is correlated with the structural changes caused by the hardening process.

Low-temperature X-ray diffraction, transport properties, specific-heat, thermal expansion and magnetic investigations of SmCu2

A variety of physical properties (low-temperature X-ray diffraction, electrical resistivity, thermal conductivity, thermopower, specific heat, thermal expansion and susceptibility) of orthorhombic SmCu2 have been studied. A significant contribution of the J=5/2 Hund ground state has been observed. An estimation of the overall crystal-field splitting obtained from the termal expansion experiment yields a value of 110 K. The magnetic entropy indicates a doublet ground state, since the observed value (Sm=5.50+or-0.2 J mol-1 K-1) is very near to the theoretical R ln 2. An additional influence of the J=7/2 multiplet is visible in the resistivity and susceptibility results. The pronounced increase of the thermal conductivity in the magnetically ordered region (Neel temperature TN=23 K) is discussed within the framework of magnon-heat conductivity.

Anomaly in the low temperature thermal expansion of alloys near the critical composition for magnetism

The thermal expansion of Ni-Cr alloys, near the critical concentration xM at which ferromagnetic order appears, shows a small characteristic anomaly below about 10 K. This anomaly increases in size as xM is approached, then abruptly changes sign going through xM. We deduce from the expansion data that the ground-state magnetovolume in the ferromagnetic Ni-Cr alloys is positive, and suggest a qualitative picture that accounts for the sign change of the anomaly. Our explanation provides support for the notion that spin fluctuations significantly affect volume. Similar behaviour appears to be seen in other alloys.

Neutron and low temperature X-ray powder diffraction and thermal expansion measurements on La1.85Sr0.15Cu1 − xZnxO4 − δ

Polycrystalline samples of La1.85Sr0.15Cu0.75Zn0.25O4 − δ were investigated by means of neutron diffraction at 10 K. Profile refinements (Rietveld-Young) confirm isotypism with the crystal structures of La1.85Sr0.15CuO4 − δ; space group Cmca, RI = 0.038. In agreement with X-ray Guinier analyses, no deviations from symmetry were observed. The oxygen deficiencies were found to be as low as δ = 0.08. The refinements furthermore revealed a statistical replacement of Cu-atoms by Zn. There is no influence on oxygen atom order and atom occupancies by the substitution of Cu by Zn-atoms.The tetragonal to orthorhombic phase transition (I4/mmm → Cmca) has been investigated as a function of temperature (60 K to room temperature) for a series of samples La1.85Sr0.15Cu1 −xZnxO4 − δ (x = 0, 0.025 and 0.06) by means of X-ray powder diffraction and by thermal expansion measurements. Both methods accordingly reveal a continuous increase of the transition temperature with increasing Cu/Zn-substitution confirming the room temperature value at a Zn-concentration of approximately 15 mol% Zn. Furthermore, as monitored by the 2θ-difference of the line splitting of the (213), reflectionst a discontinuous type of transition was revealed with increasing Zn-content, whilst the behavior of the (110)t-reflections follows a continuous second-order displacive type of phase transition.

C-axis thermal expansion of the Tl2Ba2CaCu2Ox superconductor.

The low-temperature c-axis thermal expansion of a thin-film sample of the superconducting material Tl/sub 2/Ba/sub 2/CaCu/sub 2/O/sub x/ was measured to 10 K. Based on standard ac resistance measurements, the material exhibits a detectable drop at 110 K and zero resistance at 78 K. Careful x-ray measurements between 10 and 300 K reveal a uniform, monotonic c-axis expansion of about 0.4%, similar to what has been previously found for La/sub 1.9/Ba/sub 0.1/CuO/sub 4/ and YBa/sub 2/Cu/sub 3/O/sub 7/. Although anomalous c-axis thermal expansion has been recently reported in YBa/sub 2/Cu/sub 3/O/sub 7-//sub delta/ a careful search in the vicinity of T/sub c/ failed to reveal anything unusual in this material.

Possible effects of bandstructure in properties of quasicrystals

We note that the electron per atom ratios in the known quasicrystal alloys of simple and noble metals obey rather accurately the Hume-Rothery-type relations which are characteristic for the “band” mechanism of the structural stability. If this mechanism is pronounced in the quasicrystal alloy then a number of its characteristics such as thermopower, shear constant, low-temperature thermal expansion etc. must vary sharply and peculiarly with the alloy composition. Thus experimental investigations of such concentration dependences can provide direct information on the importance of the bandstructure effects in properties of quasicrystals.

Low Temperature Heat Capacity and Thermal Expansion of KCI Containing a Low Concentration of Li+

The linear thermal expansion coefficient a from 180 mK to 36 K and the heat capacity per gram cp from 0�5 to 10 Kare reported for KCl containing approximately 100 ppm Li+. Contributions to a and cp attributable to the impurity have been identified and analysed on the basis of a model in which the Li + ions reside about 0�05 nm from the equilibrium cationic site in any of the (111) directions. There is consistent quantitative agreement with a Schottky-like term that arises from the eightfold degeneracy of the level splitting; the splitting parameter is 1� 5 K. The large (- 160) Grtineisen parameter associated with the impurity contribution is evidence for a quantum-mechanical tunnelling process, and agrees with values derived from independent measurements of the spectroscopic and dielectric responses of this system under pressure.

Low-temperature thermal expansion and specific heat of KCl containing Li tunneling states.

Thermal-expansion coefficients and specific heats have been measured in the temperature range 0.1--10 K for KCl crystals containing less than 200 ppm /sup 6/Li or /sup 7/Li. The tunneling states associated with isolated Li ions give rise to a Grueneisen parameter of GAMMA/sub Li/ = +150 +- 15 which is isotropic and independent of temperature or of Li isotope.

Large anisotropic thermal expansion and magnetostriction in the mixed-valence compound CeNi.

We present thermal-expansion and magnetostriction measurements performed at low temperature along the three symmetry axes of the orthorhombic intermediate-valence compound CeNi. The field effects are interpreted as the sum of a main contribution arising from the intermediate-valence character, which is temperature independent, and a smaller one whose temperature and field dependences are characteristic of Ce/sup 3 +/ impurities. The low-temperature thermal expansion and the main contribution to the magnetostriction are large and strongly anisotropic. The volume effects, which are larger than in the CeSn/sub 3/ reference intermediate-valence compound, are interpreted within a T/T/sub f/ scaling-law model (T/sub f/ being the fluctuation temperature) which predicts the observed temperature dependence of the thermal expansion and field dependence of the magnetostriction. The strong anisotropy, especially the unusual negative thermal expansion and perpendicular magnetostriction along b must be related mainly to the local elastic properties in which the covalent character of the 4f-5d-3d hybridization between Ce and Ni could play a predominant role.

Theory of low-temperature thermal expansion of glasses.

We have developed a theory of low-temperature thermal expansion of glasses explaining a number of existing experimental data. We assume that thermal expansion, like many other low-temperature properties of glasses, is determined by associated two-level systems (TLS's); this concept has been introduced to explain these properties by Anderson, Halperin, and Varma and by Phillips. Our theory is based on the Karpov-Klinger-Ignat'ev model of two-level systems in glasses. The deformation potential of the TLS's is calculated. We have shown that it consists of two parts: The larger part (of the order of 0.3 eV) is responsible for the observed transport properties of glasses; however, it does not contribute to the thermal expansion of glasses. The latter is caused by a relatively small second part of the deformation potential which is, within logarithmic accuracy, proportional to the TLS's interlevel spacing E.This is why at low temperatures the coefficient of thermal expansion of glasses is approximately a linear function of the temperature. Its sign is determined by a microscopic structure of the TLS. We have calculated the Gr\"uneisen parameter \ensuremath{\Gamma}. It appears to be of the order of (${\mathrm{scrE}}_{a}$/\ensuremath{\Elzxh}${\ensuremath{\omega}}_{D}$${)}^{2/3}$\ensuremath{\simeq}100, where ${\mathrm{scrE}}_{a}$ is an energy of the order of 30 eV and ${\ensuremath{\omega}}_{D}$ is the Debye frequency. Such large values of \ensuremath{\Gamma} are connected with the softness of local anharmonic potentials that produce the TLS's in glasses. Our principal result is the dependence of the coefficient of thermal expansion \ensuremath{\alpha} on the time of experiment, ${\ensuremath{\tau}}_{\mathrm{expt}}$. It is shown that if \ensuremath{\alpha}<0, then after heating glass it is at first contracted and afterwards, after the time about ${10}^{\mathrm{\ensuremath{-}}8}$ sec (at T=0.3 K), a slow expansion begins. At ${\ensuremath{\tau}}_{\mathrm{expt}\mathrm{\ensuremath{\simeq}}1}$ sec the parameter \ensuremath{\Gamma} can have the absolute value of about (1/3) of that at ${\ensuremath{\tau}}_{\mathrm{expt}\mathrm{\ensuremath{\simeq}}{10}^{\mathrm{\ensuremath{-}}8}}$ sec. Such behavior of the thermal expansion coefficient is due to the fact that the contribution of the TLS's with large relative tunnel splitting (${\ensuremath{\Delta}}_{0}$/E\ensuremath{\simeq}1) is negative while that of the TLS's with small relative tunnel splitting (${\ensuremath{\Delta}}_{0}$/E\ensuremath{\ll}1) is positive. The latter, however, have large times of relaxation which can be comparable with the time of experiment. Finally, we discuss the relative role of the TLS's and free-electron contributions to the thermal expansion of metallic glasses.

Anisotropic magnetoelastic coupling in CeNi intermediate valence compound

We present magnetostriction and thermal expansion measurements on the orthorhombic intermediate valence compound CeNi, at low temperature along the three symmetry axes. The field effects are clearly the sum of a main contribution arising from the intermediate valency character, which is temperature independent, and a smaller one whose temperature and field dependence is characteristic of Ce 3+ impurities. The low temperature thermal expansion and the main contribution to the magnetostriction are large and strongly anisotropic, the b-axis showing a particularly different behaviour. These results can be accounted for in a model based on an electronic free energy F e = − kTNf( T/ T f), where the fluctuation temperature T f (ϵ a ,ϵ b ,ϵ c ) depends on the strains ϵ a ,ϵ b ,ϵ c in a different way. In this model the anisotropies of the thermal expansion and the magnetostriction are related to strong differences between the 3 Grüneisen parameters γ λ = − ∂ In T f/∂ϵ λ. Finally, we discuss the microscopic mechanisms wchic can give rise to this behaviour.