1,721,170 research outputs found
Microporous compounds at non-ambient (P,T) conditions: mechanisms of structure deformation, phase transitions and crystal-fluid interactions
No full textMicroporous compounds are a class of open-framework materials; their structures contain cavities (in the form of channels or cages) with free diameters < 2 nm [1]. Zeolites, with their peculiar physical-chemical properties and diverse technological applications, are the most important group of this class, followed by feldspathoids and crystalline compounds with “hybrid” heterosilicate frameworks. The knowledge of the structural evolution of this class of materials under extreme conditions (i.e., high/low temperature, high pressure) is of paramount importance, especially for the potential implications in materials science and Earth sciences. Zeolites, for example, are an important bulk commodity: the world production of natural zeolites in 2016 was about 2.8 million of tons (price: 100-230 dollars per ton) and the consumption of synthetic zeolites was approximately 1.6 million of tons.
Few decades of high-temperature and high-pressure studies of zeolites disclosed that a complex interplay between the framework topology and the extraframework constituents drives the structural response to (T,P)-variations. Isostructural compounds, which differs for the extraframework population only, are an ideal target for studying how strong may be the control exerted by ions and molecules (that fill the structural cavities) on the bulk behavior of the material. An X-ray diffraction study of four end-members of the cancrinite-group of minerals (feldspathoids), conducted by in situ high-T and high-P experiments, revealed that even slight changes in the extraframework population exert a control on the mechanisms of structure deformation, which are reflected on the bulk elastic behavior of the mineral [2-5].
Microporous compounds usually accommodate isostatic compression mainly by tilting of the framework tetrahedra, around the bridging oxygen atoms, which act as hinges. However, symmetry or chemical constraints may hinder this mechanism: displacive phase transitions can occur in zeolites and zeolite-like materials, in order to accommodate thermal, pressure and chemical stresses. In this respect, the high-P behavior of SiO2-ferrierite is an interesting case study, as it undergoes, in a relatively narrow P-range, two displacive phase transitions with complex group-subgroup relationships (PmnnP121/n1(P-1)P21/n11, [6]).
In the last few years, a growing interest was devoted to the behavior of open-framework materials when compressed in the so-called “penetrating fluids”, i.e. fluids in which molecules are small enough to be intruded at high pressure into the structural cavities. Once more, SiO2-ferrierite may be considered an interesting case study. This zeolite has been compressed using three different P-media (i.e., 16:3:1 methanol:ethanol:H2O mixture, ethylene glycol and 2-methyl-2-propanol). The intrusion of the fluid molecules into the zeolite channels and cages was able to modify the bulk compressibility of the material and to prevent the transition to the P21/n11 polymorph, showing the strong control played by the extraframework population on the compressional behavior. Similar findings were also reported for other zeolites (e.g., the zeolite AlPO4-5 [7]). Several parameters were found to control the intrusion processes, among them: the sample size (e.g., powder vs. single crystal) and the kinetics of compression. The first controls the magnitude of the intrusion process, whereas the second may prevent the intrusion, as confirmed by fast-compression experiments on zeolites [6].
[1] C. Baerlocher, L.B. McCusker, D.H. Olson, Atlas of zeolite framework types, Elsevier, Amsterdam, 2007.
[2] P. Lotti, G.D. Gatta, N. Rotiroti, F. Cámara, Am. Mineral. 2012, 97, 872.
[3] P. Lotti, G.D. Gatta, N. Rotiroti, F. Cámara, G.E. Harlow, Z. Kristallogr. 2014, 229, 63.
[4] P. Lotti, G.D. Gatta, M. Merlini, M. Hanfland, Micropor. Mesopor. Mater. 2014, 198, 203.
[5] G.D. Gatta, P. Lotti, Am. Mineral. 2016, 101, 253.
[6] P. Lotti, R. Arletti, G.D. Gatta, S. Quartieri, G. Vezzalini, M. Merlini, V. Dmitriev, M. Hanfland, Micropor. Mesopor. Mater. 2015, 218, 42.
[7] P. Lotti, G.D. Gatta, D. Comboni, M. Merlini, L. Pastero, M. Hanfland, Micropor. Mesopor. Mater. 2016, 228, 158
Crystal Chemistry of Natural REE-Phosphates and Arsenates and their (T,P)-Behavior
No full textRare Earth Elements (REE, i.e. lanthanides, Y and Sc) are nowadays fundamental components in many technological applications. For their strategic importance and supply risk, REE have been included in the EU list of the so-called “critical raw materials” [1]. This has recently fostered the study of REE minerals, aiming at a deeper understanding of their crystal chemistry, formation and accumulation processes. This contribution focusses on the crystal-chemical features and (T,P)-behavior of REE phosphates and arsenates from Mt. Cervandone (Western Alps, Italy), where REE minerals are common constituents of Alpine quartz-bearing hydrothermal veins, cross-cutting pegmatitic dykes intruded in leucocratic gneisses of the metamorphic basement.
The mineral species under study are the isostructural monazite-(Ce) (ideally CePO4) and gasparite-(Ce) (CeAsO4), Sp. Gr. P21/n, hosting the larger Light REE, and the isostructural xenotime-(Y) (YPO4) and chernovite-(Y) (YAsO4), Sp. Gr. I41/amd, hosting the larger Heavy REE. They define two solid solutions characterized by the monoclinic monazite-type and the tetragonal zircon-type structures, respectively. Chemical data obatined by WDS electron microprobe analysis show that an almost complete solid solution occurs along the xenotime-chernovite tetragonal series, with Y being the dominant cation in the 8-coordinated A site followed by the HREE, whereas a strong depletion in LREE is observed. The latters populate the 9-coordinated A site in the monoclinic structure of monazite and gasparite, for which an apparent miscibility gap is observed among the end members, differently to what observed in samples from other localities [2]. Single-crystal XRD analyses on samples with different crystal chemistry pointed out the prevailing control exerted by the composition of the tetrahedra (P vs. As) on the size and disortion of the structural units and, in turn, of the unit cell volume, independently from the REE composion of the A site. In situ single-crystal and powder synchrotron XRD esperiments have been performed at high-T (Elettra, Trieste), high-P (ESRF, Grenoble; PETRA-III, Hamburg) and combined HPHT (PETRA). The interplay among the crystal chemical and structural features control the bulk response of the investigated REETO4 phases to external thermal and compressional stimuli. The results showed that the monazite-type structure is more compressibile and expandable than the tetragonal zircon-type, whereas, among the zircon-type minerals, chernovite is more compressibile than xenotime, but at high temperature xenotime shows the higher thermal expansion coefficient. In situ HPHT XRD experiments have been performed for the first time on monazite and chernovite: monazite was found to be stable within the investigated range (T < 500 °C and P < 20 GPa), whereas chernovite, which at ambient-T undergoes a phase transition to a scheelite-type polymorph at P > 8-12 GPa, at 250 ≤ T (°C) ≤ 500 preserves the zircon-type tetragonal structure at P < 20 GPa, even though with signs of structural destabilization above 12-15 GPa. A comparison with the thermo-elastic parameters reported in the literature for synthetic end members (see e.g. [2,3]) suggests that further studies on complex multi-component natural solid solutions are needed for a thorough comprehension of the structure-related properties in these minerals.
[1] G.A. Blengini, F. Mathieux, L. Mancini, M. Nyberg, H.M. Viegas Study on the EU’s list of Critical Raw Materials. Executive Summary. Publication Office of the European Commission, Luxembourg, 2020.
[2] F. Pagliaro, P. Lotti, A. Guastoni, N. Rotiroti, T. Battiston, G.D. Gatta, Mineral. Mag. 2022, 86, 150.
[3] D. Errandonea Phys. Status Solidi B. 2017, 254, 1700016
Cancrinite-group minerals at non-ambient conditions: vishnevite and davyne
No full textIsotypic minerals of the cancrinite-group share the [CAN]-framework type, built up by layers of single six-membered rings of tetrahedra centered in an “A” or “B” position, according to the ABAB stacking sequence. In order to describe a model for the thermo-elastic behavior of these isotypic compounds, we have recently investigated the high-pressure (up to ca. 8 GPa) and low-temperature (100 ≤ T (K) ≤ 293) characteristics of the (CO3)-rich end-members cancrinite {[(Na,Ca)6(CO3)1.2-1.7][Na2(H2O)2][Al6Si6O24]} and balliranoite {[(Na,Ca)6(CO3)1.2-1.7][Ca2Cl2][Al6Si6O24]}, by means of in situ single crystal X-ray diffraction. The results [1-4] showed that, though sharing a similar volume compressibility and thermal expansivity, these minerals have a different thermo-elastic anisotropy, being more pronounced in cancrinite. This is due to different (P,T)-induced structure deformation mechanisms, governed by the different coordination environment of the extraframework population within the cages. We are extending our investigation on (SO4)-rich members of the group, and in particular on vishnevite {[(Na,Ca,K)6(SO4)][Na2(H2O)2][Al6Si6O24], analogue of cancrinite} and davyne {[(Na,Ca,K)6(SO4,Cl)][Ca2Cl2][Al6Si6O24], analogue of balliranoite}. High-pressure and low-temperature in situ single-crystal X-ray diffraction experiments are currently in progress. A preliminary analysis allowed an early description of their high-pressure behavior. Vishnevite, which is apparently stable up to 7.40(2) GPa, shows a change of the compressional behavior, with an increase of compressibility, between 2.47(2)-3.83(2) GPa. Experimental data within the range 0.0001-2.47(2) GPa have been fitted with a II-order Birch-Murnaghan equation of state (II-BM EoS, K' = 4), giving the following refined elastic parameters: V0 = 733.5(4) Å3, KV0 = 51(1) GPa; a0 = 12.762(2) Å, Ka0 = 59.8(9) GPa; c0 = 5.2013(9) Å, Kc0 = 38.0(6) GPa. A III-BM EoS fit of the experimental data within the range 3.83(2)-7.40(2) gave: V0 = 757(6) Å3, KV0 = 30(3) GPa KV' = 2.6(5); a0 = 12.84(2) Å, Ka0 = 40(3) GPa, Ka' = 1.8(4); c0 = 5.33(4) Å, Kc0 = 16(3) GPa, Kc' = 3.6(5). A re-arrangement of the extra-framework population within the channels appear to control the observed change of the compressional behavior. A significantly less pronounced increase of compressibility was observed for cancrinite at 4.62(2)-5.00(2) GPa [2]. Davyne does not show any loss of crystallinity nor a change of compressional behavior up to 7.18(2) GPa. Experimental data have been fitted with a III-BM Eos, leading to the following refined parameters: V0 = 761.6(4) Å3, KV0 = 46.8(9) GPa, KV' = 3.6(3); a0 = 12.815(2) Å, Ka0 = 50.3(9) GPa, Ka' = 4.0(3); c0 = 5.355(1) Å, Kc0 = 41.6(9) GPa, Kc' = 2.9(2), showing a strong similarity with the elastic behavior of balliranoite at high pressure[4].
[1] G.D. Gatta, P. Lotti, V. Kahlenberg, U. Haefeker Miner. Mag. 2012, 76, 933.
[2] P. Lotti, G.D. Gatta, N. Rotiroti, F. Cámara Am. Mineral. 2012, 97, 872.
[3] G.D. Gatta, P. Lotti, V. Kahlenberg, Micropor. Mesopor. Mater. 2013, 174, 44.
[4] P. Lotti, G.D. Gatta, N. Rotiroti, F. Cámara, G.E. Harlow Z. Kristallogr. 2013 (in press)
Comparative thermo-elastic behaviour of the isotypic cancrinite and balliranoite
No full textThe high-pressure behaviour and the P-induced structure evolution of a natural cancrinite from
Cameroun (Na6.59Ca0.93[Si6.12Al5.88O24](CO3)1.04F0.41•2H2O, a = 12.5976(6) Å, c =5 .1168(2) Å,
space group: P63) were investigated by in situ single-crystal X-ray diffraction under hydrostatic
conditions up to 6.63(2) GPa with a diamond anvil cell[1]. The P-V data were fitted with an
isothermal Birch-Murnaghan-type equation of state (BM EoS) truncated to the 3rd-order, giving
the following elastic parameters: V0 = 702.0(7) Å3, KV0 = 51(2) GPa and KV' = 2.9(4). Linearized
BM EoS was used to fit the a-P and c-P data, giving the following parameters: a0 = 12.593(5) Å,
Ka0 = 64(4) GPa, Ka' = 4.5(9), and c0 = 5.112(3) Å, Kc0 = 36(1) GPa, Kc' = 1.9(3). A subtle change
of the elastic behaviour appears to occur at P > 4.62 GPa, and so the elastic behaviour was also
described on the basis of BM EoS valid between 0.0001 – 4.62 and 5.00 – 6.63 GPa, respectively.
The high-pressure structure refinements allowed the description of the main deformation
mechanisms responsible for the anisotropic compression of cancrinite. The low-temperature
structure evolution of the same natural cancrinite was also investigated by means of in-situ single-crystal
X-ray diffraction[2]. The V-T data exhibit a trend without any evident thermoelastic
anomaly, with a thermal expansion coefficient αV = 38(7) •10^(-6) K^(-1) (between 100 and 293 K).
Seven structure refinements showed that the same mechanisms observed at high pressure, mainly
govern the low-T structure evolution.
A study of a natural sample of balliranoite
(Na4.47Ca2.86K0.10[Si5.96Al6.04O24](CO3)0.62(SO4)0.33Cl2.03, a = 12.680(1) Å, c = 5.3141(5) Å, S.G.:
P63) at high pressure and low temperature is in progress. Preliminary P-V data up to 4.93 GPa
were fitted with a BM EoS truncated to the 2nd order (II-BM EoS), giving the following refined
parameters: V0 = 735.6(9) Å3, KV0 = 48.0(14) GPa. A fit with a II-BM EoS, applied to the P-V
data of cancrinite within the range 0.0001-4.62 GPa, gave the following parameters: V0 = 702.5(5)
Å3, KV0 = 48.8(6) GPa, showing similar volume compressibility. However, a different elastic
anisotropy is observed (Ka0:Kc0 = 2.14:1 in cancrinite; Ka0:Kc0 = 1.40:1 in balliranoite). Structure
refinements of balliranoite from high pressure and low temperature diffraction data will lead to
the description of the P/T-induced structure evolution, allowing a comparative crystal-chemistry
analysis of this class of materials.
References
1.P. Lotti, G.D. Gatta, N. Rotiroti, F. Càmara Am. Mineral. (2012), 97, 872−882.
2.G.D. Gatta, P. Lotti, V. Kahlenberg, U. Haefeker Mineral Mag. (2012, in press)
In situ synchrotron studies of open-framework silicates at non-ambient temperature and pressure
No full textThe combined use of synchrotron X-ray diffraction (XRD) techniques and devices for in situ studies at non-ambient temperature and/or pressure allowed a deep investigation of the behavior of open-framework silicates at these conditions. Displacive phase transitions are common mechanisms adopted by framework compounds to accommodate the bulk expansion or contraction, whenever structural distortion is no more possible or energetically efficient. The zeolite mordenite, for example, crystallizes, at ambient condition, in the Cmc21 space group and undergoes a P-induced transition to a primitive polymorph. In situ single-crystal synchrotron XRD allowed to identify the space group symmetry (Pbn21) of the high-P phase and solve its framework structure, allowing to describe the deformation mechanisms triggered by the phase transition at the atomic scale. In the case of minerals, the fundamental thermo-elastic parameters and their relationship with the crystal structure can be accurately determined. Scapolites are common metamorphic minerals able to accommodate volatiles down to the lower crust, which members represent a complex non-binary solid solution. Modelling the role played by the crystal chemistry on the scapolites behavior is possible by investigating the response of the solid-solution members to T and P variations. Our group recently investigated the behavior of an intermediate scapolite (with anomalous I4/m symmetry) by in situ XRD studies at high-P (ambient-T), high-T (ambient-P) and combined high-T and P, at synchrotron facilities, providing a comprehensive characterization of the elastic and structural response, as well as of a pressure-controlled phase transition to a triclinic polymorph (at ~ 9-10 GPa) observed at 25 and 650 °C. In situ synchrotron studies on framework silicates at variable P/T also allows a better understanding of phenomena, which may be exploited in materials science and technological applications, in particular promoting crystal-fluid interactions at extreme conditions. MFI-zeolites, for example, can be adopted as catalysts in the methanol-to-olefin conversion and pressure may be adopted as a tool to improve the process efficiency, by promoting a larger loading of methanol molecules into the zeolites structural pores. In situ high-P powder XRD experiments on all-silica (silicalite) and slightly cation-exchanged MFI zeolites, using non-penetrating silicone oil and penetrating methanol as P-fluids, showed a higher efficiency in methanol adsorption by pure silicalite in the lower pressure regime and, conversely, a higher methanol intrusion in cation-exchanged zeolites at P > 0.5 GPa
Behavior of B-containing ceramic materials at extreme conditions of temperature and pressure
No full textBoron is a fundamental resource for the modern society, as confirmed by the doubling in the world production of ore minerals during the last decade (US Geological Survey, 2007, 2017). The applications of boron in the ceramic industry mainly concerns the production of: i) super-hard light ceramics (e.g., B4C), ii) ultra-high temperature ceramics for extreme refractories applications, and iii) composite materials for the shielding of neutron radiation, due to the large absorption capacity of 10B (Carter et al., 1953). The understanding of the technical properties of materials at non-ambient conditions of T and P, requires the understanding of the (T, P)-induced deformation of the crystal structure at the atomic scale. In this contribution are reported three examples concerning B-containing compounds: I) synthetic mullite-type Al5BO9, II) natural londonite, and III) natural colemanite. I) The synthetic Al5BO9 compound is a commercially relevant ceramic material (Fischer & Schneider, 2008). It belongs to the group of mullite-type compounds, with crystal structures characterized by infinite chains of edge-sharing AlO6 octahedra. Al5BO9 shares with mullite (sensu stricto) several technical properties, among those: a low thermal expansion coefficient (αV0 = 1.36(2)⋅10-5 K-1, Fisch & Armbruster, 2012) and high thermal and pressure stability. In addition provides lower density (for aerospace ceramics applications) and neutron absorption capacity. Its high-P behavior was studied up to 26 GPa (Gatta et al., 2010, 2013), disclosing that the low compressibility (KV0 = 1/βV0 = 164(4) GPa, βV0 = 0.0061(1) GPa-1) and the anisotropic compression are strictly controlled by the mullite-type crystal structure. The chains of AlO6 octahedra act as pillars, which counteract the compression along the [100] direction. On the contrary, the higher compressibility on the plane perpendicular to the chains direction (100) is controlled by the occurrence of interpolyhedral tilting mechanisms. II). The high-P behavior of Al5BO9 suggests that inhibiting the tilting among the coordination polyhedra may be adopted for tuning lower compressibilities. In this respect, suitable structures can be searched among the materials provided by Nature (i.e. minerals). Londonite, for example, is a rare mineral with ideal chemical formula (Cs,K)Al4Be5B11O28, with Cs > K. Londonite is characterized by high symmetry (space group: P-43m) and a highly close-packed structure. Its high-T (Gatta et al., 2011) and high-P behaviors (Gatta et al., 2017) have been investigated by means of in situ diffraction techniques. High-P data showed that londonite is stable in its cubic symmetry at least up to 24 GPa and disclosed a significantly low compressibility (KV0 = 212(7) GPa), approaching that of carbide ceramic compounds (KV0 ~ 250 GPa). Such a stiffness is controlled by the high symmetry and close-packing of the structure, which prevent the inter-polyhedral tilting and allow the accommodation of the bulk compression only through the compression and distortion of the polyhedra. In this light, synthetic counterparts of londonite are promising materials for neutron shielding and Cs-disposal applications. III) Colemanite, CaB3O4(OH)3⋅H2O, is not a ceramic compound, but a relevant B-ore mineral. Its high-P behavior (Lotti et al., 2017) provides a window on the behavior of boron at extreme conditions. The experimental diffraction data collected up to ~ 24 GPa show the occurrence of a reconstructive phase transition at ~ 14.5 GPa. Remarkably, the phase transition induces a fraction of the boron atoms to increase their coordination from triangular to tetrahedral, by making new bonds with close H2O-oxygen atoms.
REFERENCES
Carter, R.S., Palevsky, H., Myers, V.W., Hughes, D.J. (1953): Thermal neutron absorption cross sections of boron and gold.
Phys. Rev., 92, 716-721.
Fisch, M. & Armbruster, T. (2012): Thermal Expansion of Aluminoborates. In: “Minerals as Advanced Materials II”, S.V.
Krivovichev, ed., Springer-Verlag, 255-268.
Fischer, R.X. & Schneider, H. (2008): Crystal chemistry of borates and borosilicates with mullite-type structures: a review.
Eur. J. Mineral., 20, 917-933.
Gatta, G.D., Rotiroti, N., Fisch, M., Armbruster, T. (2010): Stability at High Pressure, Elastic Behavior and Pressure-Induced
Structural Evolution of “Al5BO9”, a Mullite-Type Ceramic Material. Phys. Chem. Miner., 37, 227-236.
Gatta, G.D., Vignola, P., Lee, Y. (2011): Stability of (Cs,K)Al4Be5B11O28 (londonite) at high pressure and high temperature:
a potential neutron absorber material. Phys. Chem. Miner., 38, 429-434.
Gatta, G.D., Lotti, P., Merlini, M., Liermann, H-P., Fisch, M. (2013): High-Pressure Behavior and Phase Stability of Al5BO9,
a Mullite-Type Ceramic Material. J. Am. Ceram. Soc., 96, 2583-2592.
Gatta, G.D., Lotti, P., Comboni, D., Merlini, M., Vignola, P., Liermann, H-P. (2017): High-pressure behavior of
(Cs,K)Al4Be5B11O28 (londonite): A single-crystal synchrotron diffraction study up to 26 GPa. J. Am. Ceram. Soc.,
DOI: 10.1111/jace.14936.
Lotti, P., Gatta, G.D., Comboni, D., Guastella, G., Merlini, M., Guastoni, A., Liermann, H-P. (2017): High-pressure behavior
and P-induced phase transition of CaB3O4(OH)3⋅H2O (colemanite). J. Am. Ceram. Soc., 100, 2209-2220.
US Geological Survey (2007): Mineral Commodity Summaries. US Geological Survey, 195 p.
US Geological Survey (2017): Mineral Commodity Summaries. US Geological Survey, 202 p
Crystal-fluid interactions in erionite-group zeolites under compression
No full textIn the last two decades many studies showed that hydrostatic compression is able to enhance or induce the intrusion of molecules (or solvated ions) into the structural nano-cavities of microporous materials, pointing out that this is a viable way to promote a mass transfer from fluids to structurally-incorporated molecules. A full understanding of this phenomenon in natural or synthetic zeolites might expand the number of their utilizations, e.g. tailoring of new materials, as catalysts in industrial processes [1,2]. In addition, this phenomenon bears an intrinsic relevance also in Earth Sciences, as zeolites may act as fluid carriers in the upper Earth crust, e.g. during the early subduction of oceanic sediments or altered basalts.
In this scenario, we focused on three natural zeolites, structurally characterized by six-membered rings of tetrahedra and belonging to the large group of ABC-6 open-framework materials: erionite, offretite and bellbergite. Erionite is a quite common zeolite in nature, where it forms in basaltic vugs, crystallizing from hydrothermal fluids. It shows an ERI-type framework, made by the repetition of AABAAC sequences of 6-membered rings of tetrahedra layers. Offretite (OFF framework type) shows an AAB sequence and is commonly intergrown with erionite, due the easy occurrence of stacking faults at B and C positions of the 6-membered rings layers. Bellbergite is a rather uncommon zeolite in nature, more famous for its synthetic counterparts [3], and shows an EAB framework with ABBACC sequence.
The crystal-fluid interactions during compression were investigated by means of in situ single-crystal X-ray diffraction, which allows to focus the study on the effects that interaction has on the crystal structure of zeolites. The experiments were performed at the ID15B beamline of the European Synchrotron Radiation Facility, using diamond anvil cells to apply hydrostatic pressures on the investigated samples and using different pressure-transmitting fluids: namely, the non-penetrating silicone oil and daphne oil 7575 and potentially penetrating methanol:ethanol:water 16:3:1 mixture, ethanol:water 1:1 mixture, methanol, distilled H2O and liquid Ne. As non-penetrating are intended those fluids which molecules have a kinetic diameter larger than the free diameter of the open-framework of the zeolite and, therefore, cannot be pressure-intruded into the crystal structure. The compressional experiments in non-penetrating fluids provide, therefore, a benchmark to which compare the behavior of the same microporous compound in a potentially penetrating fluid.
Among the investigated natural samples, erionite resulted to be the one with the highest magnitude of adsorption, as shown by Figure 1. The new adsorbed molecules act as “pillars” within the framework nanocavities, decreasing the compressibility of the structure, as it is clear comparing the unit-cell vs. pressure evolution of erionite compressed in silicone oil and methanol:ethanol:water (16:3:1) mixture, respectively (Figure 1). The obtained results also allow to conclude that the magnitude of the intrusion for a given zeolite is strictly related to the H2O content of the hydrous P-transmitting fluids, where the largest is the water fraction, the highest the magnitude of the intrusion and (sometimes) the lower the pressure at which it occurs. A comparison of the crystal-fluid interactions under pressure in natural erionite and in other synthetic zeolites (e.g. SiO2-ferrierite [4]), points out that the observed magnitude of intrusion in this study is surprisingly high for a natural zeolite, characterized by channels and cages already filled by extraframework cations and molecules. These results suggest that natural zeolites, despite being intrinsically less inclined to show pressure-induced crystal-fluid interaction with respect to synthetic ones, should not be a priori excluded as targets for the tailoring of new materials by exploiting hydrostatic compression, especially when a modest temperature is also applied. Moreover, the obtained results also suggest that the role of zeolites as fluid carriers or fluid moderators in the geological processes occurring in the upper Earth crust deserves a more comprehensive characterization for a full understanding.
Acknowledgements: ESRF is acknowledged for the provision of beamtime. The Italian Ministry of Education (MUR) is acknowledged for the support through the projects “PRIN2017—Mineral reactivity, a key to understand large-scale processes” (2017L83S77) and “Dipartimenti di Eccellenza 2023-2027”.
References (up to five):
[1] G.D. Gatta, P. Lotti, G. Tabacchi, Physics and Chemistry of Minerals 45, 2018, 115–138
[2] D. Comboni, F. Pagliaro, P. Lotti, G.D. Gatta, M. Merlini, S. Milani, M. Migliori, G. Giordano, E. Catizzone, I.E. Collings, M. Hanfland, Catalysis Today 345, 2020, 88–96.
[3] R. Aiello, R.M. Barrer, Journal of the Chemical Society A, 1970, 1470-1475.
[4] P. Lotti, R. Arletti, G.D. Gatta, S. Quartieri, G. Vezzalini, M. Merlini, V. Dmitriev, M. Hanfland, Microporous and Mesoporous Materials 218, 2015, 42-54
Spin-polarized transport through a laterally coupled Aharonov–Bohm ring with two magnetic impurities
No full textWe consider spin-polarized electron transport through an Aharonov-Bohm ring threaded by magnetic flux, side coupled to a quantum waveguide. The ring contains two magnetic defects symmetrically placed with respect to the stub. In the framework of the quantum-waveguide approach, we treat the
transport process as a multi-channel scattering problem, the possible spin channels being degenerate in energy. We study both the phase coherence of the electron’s wave function, and the entanglement formation between the impurities spins due to the scattering process, in correspondence to various
initial spin configurations. To this end, we consider both a suitable spin-flip parameter, and the transmission concurrences for the outgoing state. In particular, we find that phase coherence is preserved in correspondence to the maximally entangled singlet state of the impurities, in close analogy to what has been found in the literature for a serially coupled ring
Entanglement generation in two-dimensional quantum waveguides with magnetic impurities
Full text linkWe study spin-dependent transport in a two-dimensional waveguide with two magnetic impurities. The waveguide may have a non-trivial boundary, and the electron is coupled to the defect through contact spin–spin interactions amended by a suitable form factor to avoid divergences in the transverse-mode expansion.The scattering operator is evaluated in a fully multi-channel framework,and entanglement production analyzed by studying both the transmission coefficients, and the concurrence between the defects' spin degrees of freedom. For non-entangled incoming states, entanglement production is enhanced in correspondence to resonance transmission. Differently from one-dimensional, single-channel scattering,
however, no tendency toward robust entanglement production is observed with increasing energy.On the other hand, the peculiar role played by the maximally entangled singlet state of the impurities in electron transmission is confirmed in the multichannel calculations. In this case also, the whole scenario is significantly more complex than in strictly one-dimensional systems, because of the opening of thresholds
with increasing energy, and the presence of evanescent modes, whose effects cannot be ignored
Quantum oscillations and entanglement in Aharonov–Bohm rings with two magnetic impurities and asymmetric electron injection
No full textWe study spin-polarized transport through an Aharonov-Bohm ring threaded by magnetic flux, which is serially or laterally coupled to an external waveguide. The ring contains two magnetic impurities, whose spins are coupled to the electron spin through contact spin-spin interactions. In the framework of a quantum waveguide approach, asymmetry effects in the coupling of the ring to the environment are taken into account through a suitable, unitary parametrization of the vertex scattering operator, containing an asymmetry parameter lambda and a coupling parameter epsilon For lambda = 1, epsilon = 4/9 this parametrization gives the same results as the employment of Griffith's boundary conditions. We find that asymmetry may considerably influence the transmission of maximally entangled states through the ring. To this end, we analyze both the Aharonov-Bohm oscillations of the transmission coefficients, and the entanglement between the impurities spins by means of concurrencies. We show that asymmetry is less influential in the side-coupled configuration, with respect to the serial case
- …
