Journal articles on the topic 'Post-spinel phase transition'

AbstractThe 660-kilometre seismic discontinuity is the boundary between the Earth’s lower mantle and transition zone and is commonly interpreted as being due to the dissociation of ringwoodite to bridgmanite plus ferropericlase (post-spinel transition)1–3. A distinct feature of the 660-kilometre discontinuity is its depression to 750 kilometres beneath subduction zones4–10. However, in situ X-ray diffraction studies using multi-anvil techniques have demonstrated negative but gentle Clapeyron slopes (that is, the ratio between pressure and temperature changes) of the post-spinel transition that do not allow a significant depression11–13. On the other hand, conventional high-pressure experiments face difficulties in accurate phase identification due to inevitable pressure changes during heating and the persistent presence of metastable phases1,3. Here we determine the post-spinel and akimotoite–bridgmanite transition boundaries by multi-anvil experiments using in situ X-ray diffraction, with the boundaries strictly based on the definition of phase equilibrium. The post-spinel boundary has almost no temperature dependence, whereas the akimotoite–bridgmanite transition has a very steep negative boundary slope at temperatures lower than ambient mantle geotherms. The large depressions of the 660-kilometre discontinuity in cold subduction zones are thus interpreted as the akimotoite–bridgmanite transition. The steep negative boundary of the akimotoite–bridgmanite transition will cause slab stagnation (a stalling of the slab’s descent) due to significant upward buoyancy14,15.

Crystal structures and electrochemical reactivities of high-pressure forms of the lithium titanium spinel Li[Li_1/3Ti_5/3]O₄ (LTO) were investigated under a pressure of 12 GPa to elucidate its structural phase transition from spinel to post-spinel and to obtain a wide variety of electrode materials for lithium-ion batteries.

The dependence on lithium for rising global energy demand coupled with the scarcity of lithium necessitates the exploration of post-lithium strategies. Calcium-ion batteries are one such post-lithium strategy that can mitigate rising costs owing to calcium’s natural abundancy. A critical gap in this field is the lack of cathodes capable of intercalating calcium at high voltages and capacities while also retaining structural stability. The handful of candidates evaluated thus far have been plagued by low capacities and poor cycling performance due to intercalation–induced phase changes and instability. Transition metal oxide post–spinel–type materials have been identified as potential candidates for reversible Ca–ion storage owing to their crystal structures and high theoretical energy densities. However, experimental validation of these theoretical predictions remains largely unaddressed. In this work, post-spinel Calcium Iron Oxide (CaFe2O4) and Calcium Manganese Oxide (CaMn2O4) are explored as cathodes for calcium-ion batteries. The redox activity of each cathode is investigated using galvanostatic (GS) cycling while their structural stabilities are evaluated with X-ray diffraction (XRD) and scanning electron microscopy (SEM). The use of GS in tandem with XRD and SEM provides insights into the evolution of crystal structure with Ca–ion–transport within each cathode. Our results reveal that these post–spinel systems can cycle with a reversible capacity of 56 mAh/g, making them promising cathode candidates for Ca–ion batteries and warrant further investigation.

The Clapeyron slope is the slope of a phase boundary in P–T space and is essential for understanding mantle dynamics and evolution. The phase boundary is delineating instead of balancing a phase transition’s normal and reverse reactions. Many previous high pressure–temperature experiments determining the phase boundaries of major mantle minerals experienced severe problems due to instantaneous pressure increase by thermal pressure, pressure drop during heating, and sluggish transition kinetics. These complex pressure changes underestimate the transition pressure, while the sluggish kinetics require excess pressures to initiate or proceed with the transition, misinterpreting the phase stability and preventing tight bracketing of the phase boundary. Our recent study developed a novel approach to strictly determine phase stability based on the phase equilibrium definition. Here, we explain the details of this technique, using the post-spinel transition in Mg2SiO4 determined by our recent work as an example. An essential technique is to observe the change in X-ray diffraction intensity between ringwoodite and bridgmanite + periclase during the spontaneous pressure drop at a constant temperature and press load with the coexistence of both phases. This observation removes the complicated pressure change upon heating and kinetic problem, providing an accurate and precise phase boundary.

In recent years, extensive research has been performed on high energy cathode materials for lithium ion batteries being used in electric vehicles to reduce carbon emissions. Compared to the commercial layered cathode materials, the absence of cobalt in the spinel LiMn1.5Ni0.5O4 (LMNO) makes this material more environmentally friendly and cheaper.1 Spinel LMNO cathodes also reveal attractive gravimetric and volumetric energy densities of 635Whkg−1 and 2820WhL−1, respectively.2 According to the distribution of transition metals (TM) within the cubic crystal structure, spinel LMNO can be categorized into either ordered or disordered. Normally, disordered LMNO materials are produced at temperatures higher than the theoretical oxygen release temperature of spinel LMNO (715 °C).3 The formation of O vacancies is accompanied by some Mn4+ atoms being reduced to Mn3+ to maintain the electroneutrality of spinel LMNO. Ordered LMNO can be obtained through calcination at temperatures lower than 715 °C or post-annealing disordered LMNO materials at 700 °C.4 The reversible extraction and insertion of O atoms accompanied with different distribution of TM during spinel LMNO preparation drive up a hypothesis that the oxygen activity during cycling of spinel LMNO may be affected by the distribution of TM atoms, especially since the operating voltage of spinel LMNO (> 4.7 V) is high enough to trigger oxygen redox in other lithium transition metal oxides.5 To explore the feasibility of oxygen activity during cycling of spinel LMNO, the normal, core-shell and sandwich designed synthesis are performed using special Mn0.75Ni0.25(OH)2 precursors to arrange different distributions of TM atoms in the obtained N-, CS- and SW-LMNO. As shown in Figure 1(a) – (c), the three materials show similar XRD patterns in the pristine state, yet different reflection peaks are observed in the three materials after charging to 4.9 V. The unclear phase transition of SW-LMNO indicates it show stable structure. The three materials also show different CV curves, see Figure 1(d). This indicates the extraction and insertion of Li atoms lead to different redox reactions in the three materials. Besides, differential electrochemical mass spectrometry (DEMS), in-situ transmission electron microscope (TEM) as well as hard and soft X-ray absorption spectroscopy (XAS) measurements are utilized to further investigate the oxygen activity during cycling of spinel LMNO. Reference 1. Li, M. & Lu, J. Cobalt in lithium-ion batteries. Science 367, 979-980 (2020). 2. Hagh, N. M. & Amatucci, G. G. A new solid-state process for synthesis of LiMn1. 5Ni0. 5O4−δ spinel. Journal of Power Sources 195, 5005-5012 (2010). 3. Manthiram, A., Chemelewski, K. & Lee, E.-S. A perspective on the high-voltage LiMn1.5Ni0.5O4 spinel cathode for lithium-ion batteries. Energy & Environmental Science 7, 1339-1350 (2014). 4. Chemelewski, K. R., Shin, D. W., Li, W. & Manthiram, A. Octahedral and truncated high-voltage spinel cathodes: the role of morphology and surface planes in electrochemical properties. Journal of Materials Chemistry A 1, 3347-3354 (2013). 5. Seo, D.-H. et al. The structural and chemical origin of the oxygen redox activity in layered and cation-disordered Li-excess cathode materials. Nature chemistry 8, 692-697 (2016). Figure 1. Operando X-ray diffraction patterns of N- (a), CS- (b) and SW- (c) LiMn1.5Ni0.5O4 in the pristine states and at the charge states of 4.9 V and the corresponding cyclic voltammetry curves of the three materials (d) Figure 1

The metastable olivine (Ol) wedge hypothesis assumes that Ol may exist as a metastable phase at the P conditions of the mantle transition zone (MTZ) and even deeper regions due to inhibition of the phase transitions from Ol to wadsleyite and ringwoodite caused by low T in the cold subducting slabs. It is commonly invoked to account for the stagnation of the descending slabs, deep focus earthquakes and other geophysical observations. In the last few years, several new structures with the forsterite (Fo) composition, namely Fo-II, Fo-III and Fo-IV, were either experimentally observed or theoretically predicted at very low T conditions. They may have important impacts on the metastable Ol wedge hypothesis. By performing first-principles calculations, we have systematically examined their crystallographic characteristics, elastic properties and dynamic stabilities from 0 to 100 GPa, and identified the Fo-III phase as the most likely metastable phase to occur in the cold slabs subducted to the depths equivalent to the lower part of the MTZ (below the ~600 km depth) and even the lower mantle. As disclosed by our theoretical simulations, the Fo-III phase is a post-spinel phase (space group Cmc21), has all cations in sixfold coordination at P < ~60 GPa, and shows dynamic stability for the entire P range from 0 to 100 GPa. Further, our static enthalpy calculations have suggested that the Fo-III phase may directly form from the Fo material at ~22 GPa (0 K), and our high-T phase relation calculations have located the Fo/Fo-III phase boundary at ~23.75 GPa (room T) with an averaged Clapeyron slope of ~−1.1 MPa/K for the T interval from 300 to 1800 K. All these calculated phase transition pressures are likely overestimated by ~3 GPa because of the GGA method used in this study. The discrepancy between our predicted phase transition P and the experimental observation (~58 GPa at 300 K) can be explained by slow reaction rate and short experimental durations. Taking into account the P-T conditions in the cold downgoing slabs, we therefore propose that the Fo-III phase, rather than the Ol, highly possibly occurs as the metastable phase in the cold slabs subducted to the P conditions of the lower part of the MTZ (below the ~600 km depth) and even the lower mantle. In addition, our calculation has showed that the Fo-III phase has higher bulk seismic velocity, and thus may make important contributions to the high seismic speeds observed in the cold slabs stagnated near the upper mantle-lower mantle boundary. Future seismic studies may discriminate the effects of the Fo-III phase and the low T. Surprisingly, the Fo-III phase will speed up, rather than slow down, the subducting process of the cold slabs, if it metastably forms from the Ol. In general, the Fo-III phase has a higher density than the warm MTZ, but has a lower density than the lower mantle, as suggested by our calculations.

Lithium-rich layered oxides are recognized as promising materials for Li-ion batteries, owing to higher capacity than the currently available commercialized cathode, for their lower cost. However, their voltage decay and cycling instability during the charge/discharge process are problems that need to be solved before their practical application can be envisioned. These problems are mainly associated with a phase transition of the surface layer from the layered structure to the spinel structure. In this paper, we report the AlF3-coating of the Li-rich Co-free layered Li1.2Ni0.2Mn0.6O2 (LLNMO) oxide as an effective strategy to solve these problems. The samples were synthesized via the hydrothermal route that insures a very good crystallization in the layered structure, probed by XRD, energy-dispersive X-ray (EDX) spectroscopy, and Raman spectroscopy. The hydrothermally synthesized samples before and after AlF3 coating are well crystallized in the layered structure with particle sizes of about 180 nm (crystallites of ~65 nm), with high porosity (pore size 5 nm) determined by Brunauer–Emmett–Teller (BET) specific surface area method. Subsequent improvements in discharge capacity are obtained with a ~5-nm thick coating layer. AlF3-coated Li1.2Ni0.2Mn0.6O2 delivers a capacity of 248 mAh g−1 stable over the 100 cycles, and it exhibits a voltage fading rate of 1.40 mV per cycle. According to the analysis from galvanostatic charge-discharge and electrochemical impedance spectroscopy, the electrochemical performance enhancement is discussed and compared with literature data. Post-mortem analysis confirms that the AlF3 coating is a very efficient surface modification to improve the stability of the layered phase of the Li-rich material, at the origin of the significant improvement of the electrochemical properties.

The demand for high-capacity batteries is increasing rapidly with the upcoming energetic needs of an ever increasing population, especially in the transportation sector. Lithium-ion battery (LIB) has emerged as an attractive technology, however the main restriction is his low energy density1. To make a post-transition possible the sodium-ion battery (SIB) are among the most promising alternatives due sodium is abundant, there are enormous availability and It's low cost2. Besides, the electrochemical principles governing LIB and SIB batteries are quite similar3. Nevertheless, for both emerging alternatives it is necessary to find more suitable electrode materials. Therefore, nowadays, different electrode materials have been explored to increase the capacity of those batteries. Specially, the layered-spinel structure has been used to improve the initial specific capacity and stability electrode materials. The Na-layered structure cathode facilitates Li+-ion diffusion in the structure4. Besides the incorporation of Ti4+ in the LiMn2O4 spinel phase is performed with the purpose of improving its stability by averting the Jahn-Teller effect of the Mn3+ and decreasing Mn2+ dissolution towards the electrolyte during cycling since Ti-O provides a higher binding energy (662 kJ/mol) than for Mn-O (402 kJ/mol)1. The aim of this investigation is to estimate the optimal stoichiometry in the (1-x)Li1-yNayM1-zTizO2x LiM2-zTizO4 layered-spinel by varying the concentration of Na+ and to assess the effects of the cations addition in the cycling stability of the active material. A facile sol-gel method is presented to develop new composite materials for LIB and SIB. Cathode materials were characterized by XRD, Raman, SEM, VC, EIS and charge/discharge cycling tests. Analysis of XRD patterns confirmed the existence of a spinel-layered composite where the peaks can be indexed to the cubic spinel structure ( space group) and layered structure (C 12 - m1; R-3m and P 63-mmc space group)°5. For LIB cycling was performed typically between 4.8 and 2.0V vs. Li|Li+ at a constant current of 29.0 mAg-1, equivalent to 0.1 C-rate. The stoichiometry 0,5Li0.9Na0.1Mn0.4Ni0.5Ti0.1O2-0,5LiMn1.4Ni0.5Ti0.1O4 showed an initial specific capacity, ca. 141 mAhg-1 but later it presented increasing of the specific capacity, ca. 180 mAh g-1 at 15st cycling exhibiting 98% of its charge capacity after 30st cycles. Moreover, for SIB cycling was performed typically between 4.5 and 2.0V vs. Na|Na+ at a constant current of 10.0 mAg-1, equivalent to 0.1 C-rate. In this case, the stoichiometry 0,5Li0.5Na0.5Mn0.4Ni0.5Ti0.1O2-0,5LiMn1.4Ni0.5Ti0.1O4 showed an initial specific capacity, ca. 94 mAh g- 1. Thus, by possessing interesting properties electrochemical we believe that these materials could be a potential electrode for the development of high-power rechargeable Li-ion batteries and Na-ion batteries. References N. Mosquera, F. Bedoya-Lora, V. Vásquez, F. Vásquez, and J. Calderón, Journal of Applied Electrochemistry (2021) https://doi.org/10.1007/s10800-021-01582-w. R. Klee, P. Lavela, and J. L. Tirado, Electrochimica Acta, 375 (2021). S. Rubio et al., Journal of Solid State Electrochemistry, 24, 2565–2573 (2020). L. Zheng and M. N. Obrovac, Electrochimica Acta, 233, 284–291 (2017) https://www.sciencedirect.com/science/article/pii/S0013468617304978. S. U. Vu. N and H. V, Journal of Power Sources, 355, 134–139 (2017) http://dx.doi.org/10.1016/j.jpowsour.2017.04.055. Figure 1

Abstract Introduction and geodynamic setting. – Syn-rift exhumation of mantle rocks in a continental breakup zone was highlighted along the present-day west Iberian passive margin [e.g. Boillot et al., 1988, 1995; Whitmarsh et al., 1995, 2001; Beslier et al., 1996; Brun and Beslier, 1996; Boillot and Coulon, 1998; Krawczyk et al., 1996; Girardeau et al., 1998] and along the fossil Tethyan margins [e.g. Froitzheim and Manatschal, 1996; Manatschal and Bernoulli, 1996; Marroni et al., 1998; Müntener et al., 2000; Desmurs et al., 2001]. Along the west Iberian margin, serpentinized peridotite and scarce gabbro and basalt lay directly under the sediments, over a 30 to 130 km-wide transition between the thinned continental crust and the first oceanic crust [Girardeau et al., 1988, 1998; Kornprobst and Tabit, 1988; Boillot et al., 1989; Beslier et al., 1990, 1996; Cornen et al., 1999]. The formation of a wide ocean-continent transition (OCT), mostly controlled by tectonics and associated with an exhumation of deep lithospheric levels, would be an essential stage of continental breakup and a characteristic of magma-poor passive margins. The southwest Australian margin provides an opportunity to test and to generalize the models proposed for the west Iberian margin, as both margins present many analogies. The south Australian margin formed during the Gondwana breakup in the Mesozoic, along a NW-SE oblique extension direction [Willcox and Stagg, 1990]. From north to south, the continental slope is bounded by (1) a magnetic quiet zone (MQZ) where the nature of the basement is ambiguous [Talwani et al., 1979; Tikku and Cande, 1999; Sayers et al., 2001], (2) a zone where the basement shows a rough topography associated with poorly expressed magnetic anomalies [Cande and Mutter, 1982; Veevers et al., 1990; Tikku and Cande, 1999; Sayers et al., 2001], and which is the eastward prolongation of the Diamantina Zone, and (3) an Eocene oceanic domain. The continental breakup zone is believed to be located near or at the southern edge of the MQZ [Cande and Mutter, 1982; Veevers et al., 1990; Sayers et al., 2001]. Breakup is dated at 125 Ma [Stagg and Willcox, 1992], 95 ± 5 Ma [Veevers, 1986] or at 83 Ma [Sayers et al., 2001], and followed by ultra-slow seafloor spreading until the Eocene (43 Ma), and fast spreading afterwards [Weissel and Hayes, 1972; Cande and Mutter, 1982; Veevers et al., 1990; Tikku and Cande, 1999]. The western end of the margin (fig. 1) is starved and bounded in the OCT by basement ridges where peridotite, gabbro and basalt were previously dredged [Nicholls et al., 1981]. Altimetry data [Sandwell and Smith, 1997] show that some of these ridges are continuous over 1500 km along the OCT of the south Australian margin and of the conjugate Antarctic margin. The objectives of the MARGAU/MD110 cruise (May-June 1998; [Royer et al., 1998]; fig. 2) were to define the morpho-structure and the nature and evolution of the basement in the SW Australian OCT. An area of 180 000 km2 was explored with swath bathymetry. Gravimetric data (11382 km) were simultaneously recorded whereas few single channel seismic (1353 km) and magnetic (5387 km) data were obtained due to technical difficulties. Crystalline basement rocks, made of varied and locally well-preserved lithologies, were dredged at 11 sites located on structural highs. Main results. – The bathymetric map unveils three E-W domains (fig. 2). From north to south, they are the continental slope of Australia, prolonged westward by that of the Naturaliste Plateau, a 160 km-wide intermediate flat sedimented area corresponding to the MQZ, and a 100 km-wide zone of rough E-W oriented topography which continues the Diamantina Zone (fig. 3). The first two domains are cut through in three segments by two major fracture zones (FZ), the Leeuwin FZ along the eastern side of the Naturaliste Plateau, and the Naturaliste FZ along its western flank. These NW-SE trending FZ terminate north of the E-W trending fabric of the Diamantina Zone. Accordingly, extension occurred along the NW-SE direction during the formation of the slope and of the MQZ, and then turned to N-S during the formation of the Diamantina Zone. In the Diamantina Zone, the mantle rocks dredged at Site MG-DR02 are mainly lherzolites, rich in pyroxenitic micro-layers, and pyroxenites. They contain spinel rimmed by plagioclase and locally coronas of olivine + plagioclase between opx and spinel, which suggest that they underwent some subsolidus reequilibration in the plagioclase field (fig. 4C). Westward (Site DR09), the mantle rocks are harzburgitic, with lesser pyroxenitic bandings and no plagioclase. The rocks have coarse-grained porphyroclastic textures that are locally overprinted by narrow mylonitic shear bands, and then by a cataclastic deformation, which indicate decreasing temperatures and increasing stresses during their evolution. Basalts were sampled at Sites MG-DR01, −04, −05, and together with gabbros at Sites MG-DR02, -03, -09. They have a transitional composition as shown by their REE patterns, except one sample from site MG-DR-05 which is an alkaline basalt (fig. 5). The gabbros are clearly intrusive in the peridotite at Sites DR02 and -09. They contain olivine and clinopyroxene (cpx) at Site DR02, cpx, plagioclase and hornblende at Site DR03, and cpx and amphibole or orthopyroxene or olivine at Site DR09 (fig. 4D). At that site, a tonalite containing K-feldspar and biotite and alkaline in composition (fig. 5), has also been sampled. All these plutonic rocks display either their primary magmatic textures or secondary porphyroclastic ones that are locally overprinted by mylonitic shear zones (fig. 4E). Retrograde minerals of amphibolite to greenschist facies developed during the deformation. The basalts are clearly intrusive in the gabbros at Site DR03. They are altered and exhibit porphyric textures with abundant plagioclase and plagioclase + olivine phenocrysts at Sites DR03, -04, -08, -10, and have a transitional composition (fig. 5). The nature and evolution of the peridotites and associated gabbros are compatible with an exhumation under a rift zone, on both sides of the Leeuwin FZ. It includes a mylonitic deformation which attests that these rocks underwent a shearing deformation under lithospheric conditions, in probable relation with their exhumation during the early stages of the oceanic opening. The crustal rocks are represented only by intrusive gabbros and by transitional basalts. In the MQZ, the peridotites recovered at Site MG-DR06 are mainly spinel and plagioclase lherzolites (fig. 4B) and a few pyroxenites (fig. 4A) with high temperature porphyroclastic textures. Their discovery indicates that the basement in the MQZ is not exclusively formed of thinned continental crust. Lavas sampled westward of the Leeuwin FZ at Site DR10 have also transitional compositions (fig. 5). On the Australian slope, samples dredged at Site MG-DR07 are continental quartz-bearing rocks (mostly gneisses and rare granites), some showing a high grade paragenesis (upper amphibolite to granulite facies) marked by the presence of K-feldspar, biotite, sillimanite and/or kyanite and garnet, and without primary muscovite (fig. 4G). Some of these rocks underwent an intense mylonitic shear deformation followed by post-tectonic recrystallisation or migmatization. Depending on the age of the high grade evolution (metamorphism and shearing), these rocks document either the syn-rift exhumation of lower continental crust, or the formation of the older Australian craton. On the slope of the Naturaliste Plateau, at Site DR11, rocks of oceanic origin (gabbro-diorites/dolerite/basalt; fig. 4F) were dredged together with acid rocks (gneiss and granites) of probable continental origin, some having a quartz, K-feldspar, biotite and garnet metamorphic paragenesis (fig. 4H). At that site, the transitional basalts intrude the gabbros and associated dolerites. The presence of metamorphic acid rocks indicate that the Naturaliste Plateau is likely a continental fragment that was later intruded by mafic rocks, whose origin and ages of intrusion have to be determined. Discussion and conclusions. – The retrograde tectono-metamorphic evolution of the peridotites recovered in the MQZ, which includes a reequilibration in the plagioclase field (marked by the development of olivine and plagioclase after spinel and pyroxene), is compatible with an exhumation under a rift zone [Girardeau et al., 1988; Kornprobst and Tabit, 1988; Cornen et al., 1999]. By analogy with the Iberia Abyssal Plain, the MQZ could represent a wide OCT where the mantle was exhumed and stretched mostly by amagmatic extension before the initiation of oceanic accretion [Beslier et al., 1996; Boillot and Coulon, 1998] (fig. 6). This hypothesis is supported by the tectonic structures (horsts and grabens) imaged in the seismic data over the MQZ [Boeuf and Doust, 1975]. Accordingly, the limit of the continental crust would be located at the foot of the slope, i.e. 160 km (or 250 km in the NW-SE extension direction) northward of the assumed location of the OCT at the southern edge of the MQZ. The age of the Australia-Antarctic breakup would thus be (1) older than that inferred from the magnetic anomalies (circa 95 Ma [Cande and Mutter, 1982; Veevers, 1986]), which would rather date the onset of oceanic accretion, and (2) older than the age of the breakup unconformity estimated as Santonian (83 Ma), further east, in the Great Australian Bight [Sayers et al., 2001]. The origin of the Naturaliste Plateau, continental or oceanic, is still disputed. The discovery of metamorphic rocks of probable continental origin on the southern flank of the Plateau (Site DR11) shows that it consists at least partially of rocks of the Gondwana continent. All the samples from the Diamantina Zone confirm that its basement is made of a peridotite-gabbro-basalt assemblage. The nature and age of the peridotites and of the associated magmas will help understanding the origin of this domain, which can result either from Neocomian seafloor spreading with further remobilization during the Australia-Antarctic separation, or from post-Neocomian ultra-slow seafloor spreading. Because of the omnipresence of extensive tectonic structures (fig. 3) and of the relatively small proportion of crustal rocks relative to the mantle rocks, we argue that the formation of the Diamantina Zone was mainly controlled by tectonics rather than by magmatic processes. In conclusion, the data collected along the southwest Australian margin during the MARGAU/MD110 survey evidence two major tectonic phases with formation of a wide OCT where abundant mantle rocks, in association with few mafic rocks, outcrop or lay directly beneath the sediments. The evolution of the crystalline rocks is compatible with an exhumation under a rift zone during a phase of magma-poor extension primarily controlled by tectonic processes. The domains where basement highs were sampled seem to be continuous over more than 1500 km eastward along the south Australian margin. Additional evidence on such large-scale structural continuity and on the nature of the associated basement highs may help generalizing the models for continental breakup and formation of non-volcanic passive margins, where oceanic accretion does not immediately follow continental breakup.

Background. High-dose implantation of cobalt ions into the crystal structure of natural colourless quartz was carried out. Samples of crystal plates of rock crystal from the Svetlinskoye deposit in the South Urals plane-parallel were studied. All samples were crystallographically oriented perpendicular to the symmetry axis of the third order. Cobalt implantation into quartz was carried out using an ILU-3 ion-beam accelerator along the С axis of symmetry.Aim. To determine the ranges of thermal annealing for a controlled change in the sample colour and to establish the crystal-chemical features of the changes occurring in quartz matrix due to ionbeam modification of mineral properties.Materials and methods. Implantation modes included: room temperature, residual vacuum 10–5 torr, radiation dose from 1.0×1017 to 1.5×1017 ion/cm2 at a constant ion current density of 10 μA/cm2. Post-implantation heat treatment was carried out in three stages. The control of crystallochemical changes was carried out using a highly sensitive spectrophotometer with a wide range of wavelengths.Results. It was found that the revealed absorption bands are associated with electronic transitions in cobalt ions (Со2+ and Со 3+) coordinated in the crystal matrix of implanted and heat-treated rock crystal. The formation of an independent ultradispersed spinel phase in the irradiated quartz matrix was confirmed. The newly formed phase belongs to a partially reversed cobalt spinel.Conclusions. Taking into account the quantum-optical properties of cobalt spinel (laser shutters), the method of ion-beam modification of mineral crystal structures, quartz in particular, is highly promising in terms of creating new composite materials based on natural and artificial mineral raw materials.