Majorite-Garnet Partitioning of the Highly Siderophile Elements: New Results and Application to Mars

HSE and Os isotopes are used to constrain processes such as accretion, mantle evolution, crustal recycling, and core-mantle mixing, and to constrain the timing and depth of differentiation of Mars. Although showed that the HSE contents of the martian mantle could have been established by metal-silicate equilibrium in early Mars, the role of a cooling magma ocean and associated crystallization in further fractionating the HSEs is unclear. Garnet is thought to have played an important role in controlling trace element concentrations in the martian mantle reservoirs. However, testing these models, including Os isotopes, has been hindered by a dearth of partitioning data for the HSE in deep mantle phases - majorite, wadsleyite, ringwoodite, akimotoite - that may be present in the martian mantle. We examine the partitioning behavior of HSEs between majorite garnet (gt), olivine (oliv), and silicate liquid (melt)

Polarons in Rock-Forming Minerals: Physical Implications

The existence of thermally-activated quasiparticles in amphiboles is an important issue, as amphiboles are among the main hydrous complex silicate minerals in the Earth's lithosphere. The amphibole structure consists of stripes of 6-membered TO4-rings sandwiching MO6 octahedral slabs. To elucidate the atomistic origin of the anomalous rock conductivity in subduction-wedge regions, we studied several Fe-containing amphiboles with diverse chemistry by using in situ, temperature-dependent, polarised Raman spectroscopy. The occurrence of resonance Raman scattering at high temperatures unambiguously reveal temperature-activated small polarons arising from the coupling between polar optical phonons and electron transitions within Fe2+O6 octahedra, independently of the amphibole chemical composition. The FeO6-related polarons coexist with delocalised H+; that is, at elevated temperatures Fe-bearing amphiboles are conductive and exhibit two types of charge carriers: electronic polarons with highly anisotropic mobility and H+ cations. The results from density-functional-theory calculations on the electron band structure for a selected amphibole compound with a relatively simple composition are in full agreement with experimental data. The polaron activation temperature, mobility, and polaron-dipole magnitude and alignment can be controlled by varying the mineral composition, which makes amphiboles attractive "geo-stripes" that can serve as mineral-inspired technology to design thermally-stable smart materials with anisotropic properties

Characterization and laser operation of PLD grown Yb³⁺:Y₂O₃

# Yb3+:Y2O3# Pulsed laser deposition# Characterization of Yb3+:Y2O3 thin films# Laser experiments# Outloo

Pressure-induced transformation processes in ferroelastic Pb3(P1–xAsxO4)2Pb_{3}(P_{1–x}As_{x}O_{4})_{2}, x = 0 and 0.80

The high-pressure behaviour of two represent- ative palmierite-type Pb$_3$(P$_x$As$_{1–x}$O$_4$)$_2$ ferroelastic com- pounds with x = 0 and 0.80 was analyzed by combined single-crystal X-ray diffraction and Raman spectroscopy. Single-crystal diffraction measurements on the As-rich compound Pb3(P0.20As0.80O4)2 show that it undergoes the same macroscopic monoclinic to trigonal phase transi- tion as previously observed in pure Pb$_3$(PO$_4$)$_2$ but with a significantly lower transition pressure, p$_c$ = 0.90(4) GPa for x = 0.80 as opposed to p$_c$ = 1.81(1) for x = 0.0. Syn- chrotron X-ray diffraction experiments reveal that both compounds exhibit significant diffuse scattering in a pressure interval of ~1.5 GPa above the corresponding pressure-induced transitions, indicating the persistence of monoclinic nanodomains within the macroscopically trigonal phase above the phase-transition point, similar to the high-temperature structural state. Raman spectros- copy reveal quite distinct lattice dynamics for x = 0 and x = 0.80, indicating different pathways of pressure-driven structural alteration. The pure phosphate compound shows a displacive phase transition of thermodynami- cally second-order type, whereas the As-rich compound exhibits an order-disorder phase transition with multistep structural changes on the mesoscopic scale. The pressure evolution of the Pb phonon modes as well as the broadening of the X-ray diffraction peaks suggests a further pressure-induced phase transition occurring in the range 5–7 GPa for Pb$_3$(P$_{0.20}$As$_{0.80}$O$_4$)$_2$, whilst no indication for a second phase transition up to 10 GPa was observed for Pb$_3$(PO$_4$)$_2$

The pressure-induced phase transition(s) of ZrSiO 4 : revised: Experimental proof for the existence of a new high-pressure polymorph of zircon

The existence of a new high-pressure low-symmetry (HPLS) ZrSiO 4 phase (space group I4 ¯ 2 d), which has been predicted by density-functional-theory (DFT) calculations (Stangarone et al. in Am Mineral, 2019b), is experimentally confirmed by in situ high-pressure Raman spectroscopic analysis up to 25.3 GPa. The new ZrSiO 4 polymorph is developed from zircon via a soft-mode-driven displacive phase transition. The Cochran-law-type pressure dependency of the soft-mode wavenumber reveals a zircon-to-HPLS critical pressure pc = 20.98 ± 0.02 GPa. The increase in the phonon compressibilities of the zircon hard mode near 202cm-1 at p> pr= 10.0 GPa as well as of the reidite hard mode near 349cm-1 at p< pr marks the pressure above which zircon becomes thermodynamically metastable with respect to reidite; the experimentally determined value of pr is in good accordance with the equilibrium zircon–reidite transition pressure derived from DFT simulations. However, at room temperature, there is not enough driving force to rebuild the atomic linkages and the reconstructive transition to reidite happens ∼ 1.4 GPa above pc, indicating that at room temperature, the HPLS phase is a structural bridge between zircon and reidite. The pressure dependencies of the phonon modes in the range 350--460cm-1 reveal that the reconstructive phase transition in the ZrSiO 4 system is triggered by energy resonance and admixture of hard modes from the parent and resultant phase