The bulk S elemental abundances and delta S-34 values for 83 carbonaceous chondrites (mostly CMs and CRs) and Semarkona (LL3.0) are reported. In addition, the S elemental abundances and delta S-34 values of insoluble organic material (IOM) isolated from 25 carbonaceous chondrites (CMs, CRs, and three ungrouped) are presented. The IOM only contributes 2-7% of the S to the bulk meteorites analyzed and exhibits no systematic variations. The average group bulk S abundances are similar to previous measurements. In-group variations likely reflect variations in matrix abundances, as well as parent body processes and weathering. The S and C abundances are roughly correlated and scatter about a mixing line between CI-like matrix and C-free and S-depleted chondrules. Systematic deviations from this mixing line may indicate different degrees of heating of matrix material in the nebula. There are no systematic variations in average group delta S-34 values, in contrast to what is seen for the volatile chalcophiles Zn, Te, Se, and Ag, as well as the less volatile siderophile Cu. Renormalization of the elemental and isotopic compositions indicates that the elemental and isotopic fractionations of Zn, Te, and Ag were controlled by the same process, whereas Se is intermediate in its behavior between these three elements and S. The isotopic fractionations could be associated with diffusion of volatile chalcophiles into sulfide at the end of chondrule formation. Copper appears to be distinct in its behavior from the chalcophiles, perhaps because it is more refractory and more siderophile.

Little is known about the origin of the spectral diversity of asteroids and what it says about conditions in the protoplanetary disk. Here, we show that samples returned from Cb-type asteroid Ryugu have Fe isotopic anomalies indistinguishable from Ivuna-type (CI) chondrites, which are distinct from all other carbonaceous chondrites. Iron isotopes, therefore, demonstrate that Ryugu and CI chondrites formed in a reservoir that was different from the source regions of other carbonaceous asteroids. Growth and migration of the giant planets destabilized nearby planetesimals and ejected some inward to be implanted into the Main Belt. In this framework, most carbonaceous chondrites may have originated from regions around the birthplaces of Jupiter and Saturn, while the distinct isotopic composition of CI chondrites and Ryugu may reflect their formation further away in the disk, owing their presence in the inner Solar System to excitation by Uranus and Neptune.

Valence fluctuations of Fe2+ and Fe3+ were studied in a solid solution of LixFePO4 by nuclear resonant forward scattering of synchrotron x rays while the sample was heated in a diamond-anvil pressure cell. The spectra acquired at different temperatures and pressures were analyzed for the frequencies of valence changes using the Blume-Tjon model of a system with a fluctuating Hamiltonian. These frequencies were analyzed to obtain activation enthalpies and an activation volume for polaron hopping. There was a large suppression of hopping frequency with pressure, giving an activation volume for polaron hopping of 5.8 +/- 0.7 angstrom(3). This large, positive value is typical of ion diffusion, which indicates correlated motions of polarons and Li+ ions that alter the dynamics of both. Monte Carlo simulations were used to estimate the strength of the polaron-ion interaction energy.

Phonon densities of states (DOS) of bcc alpha-(57) Fe were measured from room temperature through the 1044K Curie transition and the 1185 K fcc gamma-Fe phase transition using nuclear resonant inelastic x-ray scattering. At higher temperatures all phonons shift to lower energies (soften) with thermal expansion, but the low transverse modes soften especially rapidly above 700 K, showing strongly nonharmonic behavior that persists through the magnetic transition. Interatomic force constants for the bcc phase were obtained by iteratively fitting a Born-von Karman model to the experimental phonon spectra using a genetic algorithm optimization. The second-nearest-neighbor fitted axial force constants weakened significantly at elevated temperatures. An unusually large nonharmonic behavior is reported, which increases the vibrational entropy and accounts for a contribution of 35 meV/atom in the free energy at high temperatures. The nonharmonic contribution to the vibrational entropy follows the thermal trend of the magnetic entropy, and may be coupled to magnetic excitations. A small change in vibrational entropy across the alpha-gamma structural phase transformation is also reported.

The interplay between sodium ordering and electron mobility in NaxFePO4 was investigated using a combination of synchrotron X-ray diffraction and Mossbauer spectrometry. Synchrotron X-ray diffraction measurements were carried out for a range of temperatures between 298 and 553 K. Rietveld analysis of the diffraction patterns was used to determine the temperature of sodium redistribution on the lattice. This diffraction analysis also gives new information about the phase stability of the system. Mossbauer spectra were collected in the same temperature range. An analysis of the temperature evolution of the spectral shapes was used to identify the onset of fast electron hopping and determine the polaron hopping rate. The temperature evolution of the iron site occupancies from the Mossbauer measurements, combined with the synchrotron diffraction results; shows a relationship between the onset of fast electron dynamics and the loss of local order on the sodium sublattice.

Ab initio molecular dynamics, supported by inelastic neutron scattering and nuclear resonant inelastic x-ray scattering, showed an anomalous thermal softening of the M-5(-) phonon mode in B2-ordered FeTi that could not be explained by phonon-phonon interactions or electron-phonon interactions calculated at low temperatures. A computational investigation showed that the Fermi surface undergoes a novel thermally driven electronic topological transition, in which new features of the Fermi surface arise at elevated temperatures. The thermally induced electronic topological transition causes an increased electronic screening for the atom displacements in the M-5(-) phonon mode and an adiabatic electron-phonon interaction with an unusual temperature dependence.

Phonon partial densities of states (pDOS) of Fe-57(3) C were measured from cryogenic temperatures through the Curie transition at 460 K using nuclear resonant inelastic x-ray scattering. The cementite pDOS reveal that low-energy acoustic phonons shift to higher energies (stiffen) with temperature before the magnetic transition. This unexpected stiffening suggests strongly nonharmonic vibrational behavior that impacts the thermodynamics and elastic properties of cementite. Density functional theory calculations reproduced the anomalous stiffening observed experimentally in cementite by accounting for phonon-phonon interactions at finite temperatures. The calculations show that the low-energy acoustic phonon branches with polarizations along the [010] direction are largely responsible for the anomalous thermal stiffening. The effect was further localized to the motions of the Fe-II site within the orthorhombic structure, which participates disproportionately in the anomalous phonon stiffening.

Plants can acclimate by using tropisms to link the direction of growth to environmental conditions. Hydrotropism allows roots to forage for water, a process known to depend on abscisic acid (ABA) but whose molecular and cellular basis remains unclear. Here we show that hydrotropism still occurs in roots after laser ablation removed the meristem and root cap. Additionally, targeted expression studies reveal that hydrotropism depends on the ABA signalling kinase SnRK2.2 and the hydrotropism-specific MIZ1, both acting specifically in elongation zone cortical cells. Conversely, hydrotropism, but not gravitropism, is inhibited by preventing differential cell-length increases in the cortex, but not in other cell types. We conclude that root tropic responses to gravity and water are driven by distinct tissue-based mechanisms. In addition, unlike its role in root gravitropism, the elongation zone performs a dual function during a hydrotropic response, both sensing a water potential gradient and subsequently undergoing differential growth.