Knowing how the major chondritic components evolved and what their initial compositions were is pivotal for our understanding of the processes that shaped the early Solar System. Here, we have extended to the CR chondrites our testing of chondrule-matrix complementarity and the four-component model, i.e., two very different explanations for the bulk compositions of the carbonaceous chondrites and their components. Combining point-counting with electron microprobe analyses, we have analyzed four relatively primitive Antarctic CRs and the fall Renazzo. Our results for the abundances of chondrules and matrix are in good agreement with literature data, and confirm that these abundances vary considerably amongst the CRs (80.4 +/- 2.3 wt.% and 18.5 +/- 2.8 wt.%, respectively, in the four Antarctic CRs vs. 62.3 +/- 3.4 wt.% and 33.2 +/- 2.2 wt.% in Renazzo). The significant differences make the determination of the average properties and bulk compositions of the CRs problematic. This is particularly true for the volatile elements that were predominantly accreted in matrix. Nevertheless, all major and many minor element concentrations reported in the literature for average bulk CRs are reproduced here to better than 10%. By comparing our results to conventionally determined bulk compositions, we were able to verify the accuracy of our approach and identify elements likely affected by alteration or analytical artifacts (e.g., Ti, K, Co). Two particular compositional details of the CR chondrites investigated are (a) the relatively high contents of Mn in the chondrules compared to CO chondrules, and (b) the depletion of S in the matrix, relative to CI. In terms of the major elements Mg, Al, Si and Ca, our data suggest that unaltered chondrules and matrix exhibited CI-like relative abundances, supporting previous conclusions for the CO chondrites. Where observed, deviations of element abundances in the matrix from CI (Na, Mg, S, Ca, Fe, Ni) can be explained in terms of alteration (parent body and terrestrial) and pre-accretionary loss of forsterite and, possibly, sulfides. Overall, our results are more consistent with the predictions of the four-component model than they are with chondrulematrix complementarity. (C) 2022 Elsevier Ltd. All rights reserved.

The D/H ratio is a clue to the origin and evolution of hydrogen-bearing chemical species in Solar system materials. D/H has been observed in the coma of many comets, but most such measurements have been for gaseous water. We present the first in situ measurements of the D/H ratios in the organic refractory component of cometary dust particles collected at very low impact speeds in the coma of comet 67P/Churyumov-Gerasimenko (hereafter 67P) by the COSIMA instrument onboard Rosetta. The values measured by COSIMA are spatial averages over an approximately 35 x 50 mu m(2) area. The average D/H ratio for the 25 measured particles is (1.57 +/- 0.54) x 10(-3), about an order of magnitude higher than the Vienna Standard Mean Ocean Water (VSMOW), but more than an order of magnitude lower than the values measured in gas-phase organics in solar-like protostellar regions and hot cores. This relatively high averaged value suggests that refractory carbonaceous matter in comet 67P is less processed than the most primitive insoluble organic matter (IOM) in meteorites, which has a D/H ratio in the range of about 1 to 7 x 10(-4). The cometary particles measured in situ also have a higher H/C ratio than the IOM. We deduce that the measured D/H in cometary refractory organics is an inheritance from the presolar molecular cloud from which the Solar system formed. The high D/H ratios observed in the cometary particles challenges models in which high D/H ratios result solely from processes that operated in the protosolar disc.

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.