Experimental, phenomenological, and theoretical analyses are given of the dependence on strain of the ferromagnetic Tc of the colossal magnetoresistance (CMR) rare earth manganese perovskites. It is found that Tc is extremely sensitive to biaxial strain; by implication other physical properties are also. The results indicate that biaxial strain is an important variable which must be considered in the design of devices based on thin films and provide evidence in favor of the relevance of the Jahn–Teller electron-phonon coupling to the CMR phenomenon.

Using neutron pair distribution function analysis over the temperature range from 1000 to 15 K, we demonstrate the existence of local polarization and the formation of medium-range, polar nanoregions (PNRs) with local rhombohedral order in a prototypical relaxor ferroelectric Pb(Mg(1/3)Nb(2/3))O3. We estimate the volume fraction of the PNRs as a function of temperature and show that this fraction steadily increases from 0% to a maximum of approximately 30% as the temperature decreases from 650 to 15 K. Below T approximately 200 K the volume fraction of the PNRs becomes significant, and PNRs freeze into the spin-glass-like state.

Thirty-two second time histories comparing vertical accelerations measured on a pier (location 3) and on the plate girder (location 1).

Resonant ultrasound spectroscopy has been used to characterize elastic softening and anelastic dissipation processes associated with the Pm3m <--> R3c transition in single crystal and ceramic samples of LaAlO(3). Softening of the cubic structure ahead of the transition point is not accompanied by an increase in dissipation but follows different temperature dependences for the bulk modulus, (1/3)(C(11) + C(12)), and the shear components, (1/2)(C(11) + C(12)) and C(44), as if the tilting instability contains two slightly different critical temperatures. The transition itself is marked by the complete disappearance of resonance peaks (superattenuation), which then reappear below ∼700 K in spectra from single crystals. Comparisons with low frequency, high stress data from the literature indicate that the dissipation is not due to macroscopic displacement of needle twins. An alternative mechanism, local bowing of twin walls under low dynamic stress, is postulated. Pinning of the walls with respect to this displacement process occurs below ∼350 K. Anelasticity maps, analogous to plastic deformation mechanism maps, are proposed to display dispersion relations and temperature/frequency/stress fields for different twin wall related dissipation mechanisms. These allow comparisons to be made of anelastic loss mechanisms under mechanical stress with elastic behaviour observed by means of Brillouin scattering at high frequencies which might also be related to microstructure.

The effects of grain size on the elastic properties of quartz through the α–β phase transition have been investigated by resonant ultrasound spectroscopy. It is found that there are three regimes, dependent on grain size, within which elastic properties show different evolutions with temperature. In the large grain size regime, as represented by a quartzite sample with ∼100–300 µm grains, microcracking is believed to occur in the vicinity of the transition point, allowing grains to pull apart. In the intermediate grain size regime, as represented by novaculite (1–5 µm grain size) and Ethiebeaton agate (∼120 nm grain size), bulk and shear moduli through the transition follow closely the values expected from averages of single crystal data. The novaculite sample, however, has a transition temperature ∼7 °C higher than that of single crystal quartz. This is assumed to be due to the development of internal pressure arising from anisotropic thermal expansion. In the small grain size region, agates from Mexico (∼65 nm) and Brazil (∼50 nm) show significant reductions in the amount of softening of the bulk modulus as the transition point is approached from below. This is consistent with a tendency for the transition to become more second order in character. The apparent changes towards second order character do not match quantitative predictions for samples with homogeneous strain across elastically clamped nanocrystals, however. Some of the elastic variations are also due to the presence of moganite in these samples. True ‘nanobehaviour’ for quartz in ceramic samples thus appears to be restricted to grain sizes of less than ∼50 nm.

The temperature and pressure dependence of the thermal displacements and lattice parameters were obtained across the γ → α phase transition of Ce using high-pressure, high-resolution neutron and synchrotron x-ray powder diffraction. The estimated vibrational entropy change per atom in the γ → α phase transition, ∆S γ−α vib ≈ (0.75±0.15)kB, is about half of the total entropy change. The bulk modulus follows a power-law pressure dependence which is well described using the framework of electron-phonon coupling. These results clearly demonstrate the importance of lattice vibrations, in addition to the spin and charge degrees of freedom, for a complete description of the γ → α phase transition in elemental Ce.PACS numbers: 64.70. Kb, 71.27.+a, 61.12.Ld Materials with electrons near the boundary between itinerant and localized behavior continue to present a major theoretical challenge to a complete description of their properties, including multiple phases and anomalous thermodynamics. This is particularly true in the 4f and 5f systems, where this boundary appears to occur in or near the elements Ce and Pu, respectively [1]. In Pu, which possesses five allotropic phases at ambient pressure, a partial localization of some of the five 5f electrons appears necessary to understand the higher temperature phases [2]. Partial localization may also be present in U compounds [3]. Ce metal is in principle simpler, possessing only a single 4f electron, but still displays four different phases at ambient pressure. One of the most interesting and still not completely understood phenomena in Ce is the isostructural (fcc) γ → α phase transition, which involves about 17% volume collapse at room temperature and pressure of roughly 0.8 GPa [4].In the majority of theoretical models [4,5,6,7,8,9, 10] the γ → α transition has been attributed to an instability of the single 4f 1 electron. The earliest models focused on charge instability, while later models dealt with spin instability. The promotional model postulates a transition from 4f 1 5d 1 6s 2 (γ-phase) to 4f 0 5d 2 6s 2 (α-phase), but is inconsistent with the 4f binding energy and the cohesive energies of other 5d 2 6s 2 materials [5]. In the Mott transition (MT) model [5,6] the 4f electron in the γ phase is localized and non-binding, but is itinerant and binding in the lower volume α phase. The energy for the phase transition is provided by the kinetic energy of the itinerant f electron. In the Kondo-volumecollapse (KVC) model [9, 10] the 4f electron is assumed to be localized in both the γ and α phases, and the phase transition is driven by the Kondo spin fluctuation energy and entropy within the context of the single-impurity Anderson model. These early models ignored altogether an explicit treatment of the lattice degrees of freedom; even the lattice entropy is not considered. More recent treatments [8,11,12] include both the lattice and spin entropies, but still do not deal explicitly with the consequences of electron-lattice coupling despite the large volume collapse at t...

The surface potential variations of the following conductors have been measured over a 0.7 cm2 area: bronze, NiP, conducting polymer (polyaniline), Al, Cu, Au, and graphite. The measurements were performed with a Kelvin probe of spatial and potential resolution of 1.5 mm and 1 mV, respectively. Subjecting the surfaces to no cleaning procedure other than a low temperature ultrahigh vacuum bake, we find a wide spectrum of variation in surface potential uniformity, with alloys typically the least uniform and nonreactive surfaces such as gold and graphite the most uniform (no fluctuations above the 1 mV probe sensitivity). Application of these results to the Los Alamos antiproton gravity experiment is discussed.

There are currently proposals to test the weak equivalence principle for antimatter by studying the motion of antiprotons, negative hydrogen ions, positrons, and electrons under gravity. The motions of such charged particles are affected by residual gas, radiation, and electric and magnetic fields, as well as gravity. The electric fields are particularly sensitive to the state of the "shielding" container. This paper reviews, and extends where necessary, the physics of these extraneous influences on the motion of charged particles under gravity. The effects considered include residual gas scattering; wall potentials due to patches, stress, thermal gradients, and contamination states; and image-charge-induced dissipation.