Sapphire dilatometer cell for measuring the thermal expansion of solids.

Capacitive-based dilatometry is used to determine the thermal expansion of solid specimens over a broad temperature range and for the study of structural and thermodynamic phase transitions. It can detect length changes of 0.1 Å or better. Dilatometer cells have been constructed of metals, such as copper or silver, and non-metals, such as silicon and fused silica. Sapphire is a good candidate for the construction of a dilatometer cell. It has excellent thermal conductivity, a well-behaved thermal expansion of moderate magnitude, especially below ∼60 K, and is readily available. The design, fabrication, and testing of a sapphire dilatometer cell are described herein.

Economical Laue x-ray diffraction using photographic film and orientation of single crystals.

Many Laue x-ray diffraction systems using the Polaroid XR-7 Land Diffraction Cassette camera became inactive after production of the required high sensitivity Polaroid T-57 instant film ceased. This Tutorial reports on a low-cost solution using the readily available replacement film with push processing to increase the effective film speed. The use of this film in the polaroid camera is described along with film development and digitization. The orientation of single crystals with the obtained data and free software is explained. A simple method to prepare single crystals with surfaces perpendicular to a desired crystallographic orientation is described. The content of this Tutorial may prove beneficial for educational and research laboratories.

Thermal Expansion of Single-Crystal H_{2}O and D_{2}O Ice Ih.

Thermal expansion of H_{2}O and D_{2}O ice Ih with relative resolution of 1 ppb is reported. A large transition in the thermal expansion coefficient at 101 K in H_{2}O moves to 125 K in D_{2}O, revealing one of the largest-known isotope effects. Rotational oscillatory modes that couple poorly to phonons, i.e., lattice solitons, may be responsible.

Magnetic, thermal, and optical properties of single-crystalline CoTa2O6 and FeTa2O6 and their anisotropic magnetocaloric effect.

The magnetic, thermal, and optical properties of single-crystalline CoTa2O6 and FeTa2O6 are reported. Optical dichroism was observed in CoTa2O6. Magnetic susceptibility χ(T) measurements reveal long-range antiferromagnetic order with Néel temperatures [Formula: see text] K and 8.11(5) K, respectively, and anisotropy in χ. The thermal expansion coefficients exhibit significant anisotropy and the influence of the magnetic ions and long-range order. A structural phase transition to orthorhombic occurs below T N for FeTa2O6. Magnetic field H lowers T N with its affect largest when H is directed along either [1 1 0] or [1 [Formula: see text] 0], and smallest when directed along [0 0 1]. This leads to an anisotropic magnetocaloric effect that is investigated through measurements of the specific heat and magnetization in applied magnetic field.

Extreme thermopower anisotropy and interchain transport in the quasi-one-dimensional metal Li0.9Mo6O17.

Thermopower and electrical resistivity measurements transverse to the conducting chains of the quasi-one-dimensional metal Li0.9Mo6O17 are reported in the temperature range 5≤T≤500 K. For T≥400 K the interchain transport is determined by thermal excitation of charge carriers from a valence band ∼0.14 eV below the Fermi level, giving rise to a large, p-type thermopower that coincides with a small, n-type thermopower along the chains. This dichotomy-semiconductorlike in one direction and metallic in a mutually perpendicular direction-gives rise to substantial transverse thermoelectric effects and a transverse thermoelectric figure of merit among the largest known for a single compound.

Magnetic and thermal responses triggered by structural changes in the double perovskite Sr2YRuO6.

Among double perovskites, the interpretation of the magnetic, thermal and transport properties of Sr(2)YRuO(6) remains a challenge. Characterization using different techniques reveals a variety of features that are not understood, described as anomalous, and yields contradictory values for several relevant parameters. We solved this situation through detailed susceptibility, specific heat, thermal expansion and x-ray diffraction measurements, including a quantitative correlation of the parameters characterizing the so-called anomalies. The emergence of short-range magnetic correlations, surviving well above the long-range transition, naturally accounts for the observed unconventional behavior of this compound. High resolution x-ray powder diffraction and thermal expansion results conclusively show that the magnetic and thermal responses are driven by lattice changes, providing a comprehensive scenario in which the interplay between the spin and structural degrees of freedom plays a relevant role.

Giant Nernst effect and bipolarity in the quasi-one-dimensional metal Li0.9Mo6O17.

The Nernst coefficient for the quasi-one-dimensional metal, Li{0.9}Mo{6}O{17}, is found to be among the largest known for metals (ν≃500 µV/KT at T∼20 K), and is enhanced in a broad range of temperature by orders of magnitude over the value expected from Boltzmann theory for carrier diffusion. A comparatively small Seebeck coefficient implies that Li{0.9}Mo{6}O{17} is bipolar with large, partial Seebeck coefficients of opposite sign. A very large thermomagnetic figure of merit, ZT∼0.5, is found at high field in the range T≈35-50 K.

Observation of a martensitic structural distortion in V, Nb, and Ta.

Thermal-expansion measurements of the Group 5 elements V, Nb, and Ta reveal a structural distortion below 300 K. Data for single-crystalline Nb and Ta display anisotropic thermal expansion, martensitic in character, that is inconsistent with cubic crystal structures at low temperature. Published results on V show similar behavior. Interstitial impurities suppress the transition.

Giant electrothermal conductivity and spin-phonon coupling in an antiferromagnetic oxide.

The application of weak electric fields ( less, similar 100 V/cm) is found to dramatically enhance the lattice thermal conductivity of the antiferromagnetic insulator CaMnO3 over a broad range of temperature about the Néel ordering point (125 K). The effect is coincident with field-induced detrapping of bound electrons, suggesting that phonon scattering associated with short- and long-ranged antiferromagnetic order is suppressed in the presence of the mobilized charge. This interplay between bound charge and spin-phonon coupling might allow for the reversible control of spin fluctuations using weak external fields.

Capacitive-based dilatometer cell constructed of fused quartz for measuring the thermal expansion of solids.

A dilatometer cell that can detect sub angstrom changes in the length of solid specimens in the temperature range 5 K

Dimensional crossover in the purple bronze Li0.9Mo6O17.

Thermal expansion of Li0.9Mo6O17 is a-axis dominated which reduces the separation of the conducting chains at low temperature enhancing the interchain coupling. This destabilizes the Luttinger-liquid fixed point leading to an electronic charge- (or spin-) density wave dominated by Coulomb repulsion, as predicted by theories for Luttinger liquids.

Universal relationship between magnetization and changes in the local structure of La1-xCaxMnO3: evidence for magnetic dimers.

We present extensive x-ray absorption fine structure measurements on La(1-x)Ca(x)MnO(3) as a function of the B field (to 11 T) and Ca concentration, chi(21%-45%). These results reveal local structure changes (associated with polaron formation) that depend only on the magnetization for a given sample, irrespective of whether the magnetization is achieved through a decrease in temperature or an applied magnetic field. Furthermore, the relationship between local structure and magnetization depends on the hole doping. A model is proposed in which a filamentary magnetization initially develops via the aggregation of pairs of Mn atoms involving a hole and an electron site. These pairs have little distortion and it is likely that they form at temperature T(*) above T(c).

Method for analyzing second-order phase transitions: application to the ferromagnetic transition of a polaronic system.

A new method for analyzing second-order phase transitions is presented and applied to the polaronic system La(0.7)Ca(0.3)MnO3. It utilizes heat capacity and thermal expansion data simultaneously to correctly predict the critical temperature's pressure dependence. Analysis of the critical phenomena reveals second-order behavior and an unusually large heat capacity exponent.

Dramatic changes in the magnetic coupling mechanism for La-doped CaMnO3.

The exchange interactions in polycrystalline samples of Ca1-xLaxMnO3 (0.00< or =x< or =0.05) are studied by means of Raman scattering and electron paramagnetic resonance. Dramatic reductions in the spin-phonon interactions and magnetic correlations are observed for La doping levels as small as approximately 2%-3%. These results show that the charge carriers play an important role in the overall exchange coupling in the electron-doped manganites, even at very low doping levels.