Paraskevas Parisiades | Sorbonne University (original) (raw)
Papers by Paraskevas Parisiades
Журнал технической физики, 2019
Phase transitions in lead hafnate (PbHfO3) at high temperature and high pressure were studied by ... more Phase transitions in lead hafnate (PbHfO3) at high temperature and high pressure were studied by single-crystal diffraction and diffuse scattering of synchrotron radiation, using heated diamond anvil cell. Measurements were carried out in the temperature range 182 ° С
Physica C: Superconductivity and its Applications, 2019
Physics of the solid state, 2023
<p>Mars&#8217; mantle dynamical history has certainly been dominated by a s... more <p>Mars&#8217; mantle dynamical history has certainly been dominated by a stagnant-lid regime, with limited mixing and homogenization. Accordingly, the chemical and mineralogical signatures of early processes, including the crystallization of a primitive magma ocean, are overall well preserved on Mars. The major geological structures visible at its surface are the remains of an intense ancient volcanism, not so dissimilar from the large igneous provinces found on Earth at very old ages (several million/billion years).</p><p>Current models used to determine the mantle thermal evolution and the crustal extraction heavily relies on melting properties of materials expected to form the Martian mantle, which, however are poorly known. In particular, the fact that the Martian mantle is probably richer in iron than the terrestrial mantle has a direct impact on the solidus and liquidus and on the chemistry of the magmas that can be produced at different pressures. Thus, the study of Martian volcanism and thermal history requires a precise understanding of the melting properties of the mantle (solidus, liquidus and extent of melting) as a function of pressure and temperature. Studies in literature are scant, mainly address the solidus, and are limited to analysis of recovered samples, missing in situ diagnostics.</p><p>To address this problem, we studied the solid-liquid melting relations and, more generally, the melting diagram for a mineralogical assemblage model of mantle composition, by high-pressure and high-temperature experiments in multi anvil press performed at the PSICHE beamline of the SOLEIL synchrotron. We determined the solidus and the liquidus of the investigated rock at pressures up to 12 GPa by complementary in-situ diagnostics (X-ray diffraction and falling sphere technic). The obtained solidus and liquidus are well lower (difference >200K), especially at the highest investigated pressures, compared to previous studies, with strong implications for the origin of volcanism and notably the crystallization of the magma ocean. Furthermore, our experiments provide important data to refine the extent of melting (&#934;), modal proportion and the chemistry of all the different phases present between the solidus and the liquidus at different conditions (P, T, &#934;).</p><p>Altogether, these new results are critical to constrain models of thermal evolution and crust extraction and formation, as well as to address the evolution of the magmatism and volcanism at the Mars surface since 3.5 Ga. Finally, depending on different parameters, such as the thickness of the crust or the concentration of radioactive elements, the estimated areotherm could cross the solidus and lead to partial melting of the mantle, especially close to the core-mantle boundary, where a high extent of melting could be reached.</p><div> <div> <div>&#160;</div> </div> </div>
Bulletin of the American Physical Society, Jul 8, 2013
Physical Review E, 2017
We report experimental evidence for a crossover between a liquid-like state and a gas-like state ... more We report experimental evidence for a crossover between a liquid-like state and a gas-like state in fluid methane (CH4). This crossover is observed in all of our experiments, up to 397 K temperature; 2.1 times the critical temperature of methane. The crossover has been characterized with both Raman spectroscopy and X-ray diffraction in a number of separate experiments, and confirmed to be reversible. We associate this crossover with the Frenkel line-a recently hypothesized crossover in dynamic properties of fluids extending to arbitrarily high pressure and temperature, dividing the phase diagram into separate regions where the fluid possesses liquid-like and gas-like properties. On the liquid-like side the Raman-active vibration increases in frequency linearly as pressure is increased, as expected due to the repulsive interaction between adjacent molecules. On the gas-like side this competes with the attractive Van der Waal's potential leading the vibration frequency to decrease as pressure is increased.
2019 IEEE International Conference on Electrical Engineering and Photonics (EExPolytech)
We report the high-temperature and high-pressure single-crystal x-ray diffraction study of PbHfO3... more We report the high-temperature and high-pressure single-crystal x-ray diffraction study of PbHfO3. The increase of pressure enables an additional intermediate phase, located between the cubic and incommensurate phases, and characterized by superstructure reflections indicating the presence of anti-phase oxygen octahedral tilts. The temperature-dependent diffuse peak at an incommensurate position is much better pronounced at higher pressures (~ 2 GPa) than at lower pressures (~ 1.1 GPa), which we interpret as enhancing of the incommensurate soft mode on pressure increase. Several peculiarities in the behavior of superstructural reflections at M- and X- points are reported and discussed.
Physics and Chemistry of Minerals
AGU Fall Meeting Abstracts, Dec 16, 2020
Physics of the Earth and Planetary Interiors, 2017
At higher pressures, the slope of the (Fe,Al)-bearing Bg melting curve remains fairly constant up... more At higher pressures, the slope of the (Fe,Al)-bearing Bg melting curve remains fairly constant up to the CMB pressure of 135 GPa, which contrasts with the flattening reported for MgSiO 3. This makes the different available results to converge to a temperature of 5100-5500 K for the melting of Bg at the CMB. We remind that the melting curve of MgSiO 3-Bg should always plot at higher temperature than that of the (Fe,Al)-bearing composition, due to the incompatible character of Fe and Al. Thus, our experimental determination of the (Fe,Al)-bearing Bg melting curve implies that the melting temperature of MgSiO 3-Bg at very high mantle pressures was underestimated by a couple hundred degrees in some previous studies (de Koker and Stixrude, 2009; Mosenfelder et al., 2009). Thus, for further discussions, we will choose the higher melting curve of MgSiO 3 Bg as determined from ab initio calculations (Stixrude and Karki, 2005). It can be modeled using a modified Simon and Glatzel equation [T=T 0 (P/a + 1) 1 / c ] with parameters T 0 =91 K, a=0.00125 GPa and c=2.83 (Simon and Glatzel, 1929). We note that the liquidus temperature profile reported previously for peridotite (Fiquet et al., 2010) appears superimposed with the melting curve of MgSiO 3-Bg derived from ab initio calculations and shock experiments (Figure 1). This is unexpected because (i) the more complex chemical composition of the Bg phase itself, compared to MgSiO 3 , and (ii) additional Fp and CaSiO 3-perovskite (CaPv) phases should both lower the peridotite liquidus below the melting temperature of pure MgSiO 3. In their study, (Fiquet et al., 2010) observed large crystals of Bg at the center of the heated spot, where the melting behavior was monitored using in situ X-ray diffraction. Chemical composition of Bg grains measured at different locations on a sample synthesized at ~61 GPa show Fe/(Mg+Fe) and Al/Si ratios of ~2.5% and ~8%, respectively. It is possible that their reported measurements of the peridotite liquidus correspond in fact to the melting curve of these large grains of MgSiO 3-bearing Bg. 3.4. VOLUME OF BRIDGMANITE MELTING
AIP Advances, 2016
We report a detailed high pressure study on Eu 1-x Sr x TiO 3 polycrystalline samples using synch... more We report a detailed high pressure study on Eu 1-x Sr x TiO 3 polycrystalline samples using synchrotron x-ray diffraction. We have observed a second-order antiferrodistortive phase transition for all doping levels which corresponds to the transition that has been previously explored as a function of temperature. The analysis of the compression mechanism by calculating the lattice parameters, spontaneous strains and tilt angles of the TiO 6 octahedra leads to a high pressure phase diagram for Eu 1-x Sr x TiO 3 .
Physical Review B, 2015
The structural transformation of multiferroic EuTiO3 has been intensively investigated by synchro... more The structural transformation of multiferroic EuTiO3 has been intensively investigated by synchrotron x-ray diffraction at pressures up to 50.3 GPa and temperatures from 50 to 500 K. An antiferrodistortive phase transition from cubic Pm-3m to tetragonal I4/mcm space group has been observed, identical to the one that has been previously explored at ambient pressure and low temperatures. Several compression/decompression cycles at different temperatures have been carried out to accurately map the transition, and as a result a P-T phase diagram for EuTiO3 has been constructed. The observed phase transition exhibits many similarities with isostructural SrTiO3, although the absence of magnetoelectric interactions in the latter accounts for the different phase boundaries between the two materials.
Physical Review B, 2014
SrMnO 3 is a perovskite compound which, unlike most perovskites, can be synthesized in three diff... more SrMnO 3 is a perovskite compound which, unlike most perovskites, can be synthesized in three different but closely related polymorphs. In this paper, the first experimental equation of state of the 6H polymorphs is reported. The experimentally determined bulk modulus of SrMnO 3 increases from 115.6(11) GPa in the 4H polymorph to 143.7(17) GPa in the 6H polymorph, while DFT calculations predict a further increase to 172.5(4) GPa in the 3C polymorph. The first in situ observations of transformations between the three known polymorphs, under high pressure and high temperature conditions are also reported. The results are compared with extensive DFT calculations and literature, and it is demonstrated that the 6H polymorph is the thermodynamically stable phase between 5.9(3) and 18.1(2) GPa at zero kelvin. The effect of possible oxygen sub-stoichiometry is also explored, used DFT. Finally, the findings are combined with the existing knowledge of the phase behavior in this system to outline where further knowledge needs to be collected before a PT phase diagram can be constructed for this system.
Physica C: Superconductivity and its Applications, 2007
We have studied the effect of aluminum doping and boron isotopic substitution on the Raman spectr... more We have studied the effect of aluminum doping and boron isotopic substitution on the Raman spectra of the Mg 1Àx Al x 10,11 B 2 polycrystalline compounds. Our data show that new peaks appear at 740and870cmAˋ1whilethebroadbandat740 and 870 cm À1 while the broad band at 740and870cmAˋ1whilethebroadbandat600 cm À1 diminishes for higher Al doping levels. The high energy band evolves to the E 2g phonon mode of AlB 2 corresponding to a strong reduction in the electron-phonon coupling. The isotopic shift for the broad band at $600 cm À1 is small considering the isotopic shift of the other bands, which follow the harmonic mass law. This extreme anharmonic behavior indicates that the broad band may not be directly related with the E 2g phonon of the B atoms.
Physica C: Superconductivity and its Applications, 2008
A systematic Raman study has been carried out on single crystals of Mg(B 1Àx C x) 2 with carbon c... more A systematic Raman study has been carried out on single crystals of Mg(B 1Àx C x) 2 with carbon concentrations in the range of x = 0.0-0.15. We have found remarkable differentiations of the Raman spectra with doping. Even with small amounts of carbon substitution (x = 0.027) the E 2g-symmetry broad band at 600cmAˋ1(forpureMgB2)diminishesandnewmodesappearoftheapproximateA1g/B1g(600 cm À1 (for pure MgB 2) diminishes and new modes appear of the approximate A 1g /B 1g (600cmAˋ1(forpureMgB2)diminishesandnewmodesappearoftheapproximateA1g/B1g(750 cm À1) and E 2g ($850 cm À1) symmetries, though the transition temperature is only slightly reduced (<2 K). The broad band does not evolve continuously into the mode of same symmetry at 850cmAˋ1,asassumedbyotherinvestigators.Thepracticaldisappearanceoftheoriginal850 cm À1 , as assumed by other investigators. The practical disappearance of the original 850cmAˋ1,asassumedbyotherinvestigators.Thepracticaldisappearanceoftheoriginal600 cm À1 mode at x ' 0.08 coincides with the fast reduction of T c. The doping dependence of the phonons indicates a two-mode behavior, which could be driven by the 2D-3D electronic topological transition and associated with a possible nanoscale phase separation.
Journal of Physics: Condensed Matter, 2008
A phase separation driven by the negative compressibility of the electron gas, near electronic to... more A phase separation driven by the negative compressibility of the electron gas, near electronic topological transitions (ETT), could drive the system at the verge of a catastrophe. We show here that the metastable phases very close to the ETT transition are observed in a mesoscopic phase separation (MePhS) driven by the quenched lattice disorder. By using high resolution synchrotron radiation x-ray powder diffraction we have identified the MePhS for the intermetallic ternary Mg 1−x Al x B 2 in the proximity of two ETTs: the first at x 1 = 0.1 and the second at x 2 = 0.3. We have identified the competition between a first 'relaxed' (R) hole poor and a second 'tense' (T) hole rich phase, and by micro-Raman we observe the splitting of the in-plane phonon E 2g mode in the proximity of the first ETT at x = 0.1. The anisotropic quenched disorder due to a random distribution of Al 3+ and Mg 2+ ions both in the axial (c axis) direction and planar (ab plane) direction, probed by x-ray diffraction and Raman data, is proposed to be the physical variable that allows the formation of metastable phases near the critical points of electronic topological transitions, where Feshbach shape resonances in interband pairing amplifies the superconducting critical temperature.
Журнал технической физики, 2019
Phase transitions in lead hafnate (PbHfO3) at high temperature and high pressure were studied by ... more Phase transitions in lead hafnate (PbHfO3) at high temperature and high pressure were studied by single-crystal diffraction and diffuse scattering of synchrotron radiation, using heated diamond anvil cell. Measurements were carried out in the temperature range 182 ° С
Physica C: Superconductivity and its Applications, 2019
Physics of the solid state, 2023
<p>Mars&#8217; mantle dynamical history has certainly been dominated by a s... more <p>Mars&#8217; mantle dynamical history has certainly been dominated by a stagnant-lid regime, with limited mixing and homogenization. Accordingly, the chemical and mineralogical signatures of early processes, including the crystallization of a primitive magma ocean, are overall well preserved on Mars. The major geological structures visible at its surface are the remains of an intense ancient volcanism, not so dissimilar from the large igneous provinces found on Earth at very old ages (several million/billion years).</p><p>Current models used to determine the mantle thermal evolution and the crustal extraction heavily relies on melting properties of materials expected to form the Martian mantle, which, however are poorly known. In particular, the fact that the Martian mantle is probably richer in iron than the terrestrial mantle has a direct impact on the solidus and liquidus and on the chemistry of the magmas that can be produced at different pressures. Thus, the study of Martian volcanism and thermal history requires a precise understanding of the melting properties of the mantle (solidus, liquidus and extent of melting) as a function of pressure and temperature. Studies in literature are scant, mainly address the solidus, and are limited to analysis of recovered samples, missing in situ diagnostics.</p><p>To address this problem, we studied the solid-liquid melting relations and, more generally, the melting diagram for a mineralogical assemblage model of mantle composition, by high-pressure and high-temperature experiments in multi anvil press performed at the PSICHE beamline of the SOLEIL synchrotron. We determined the solidus and the liquidus of the investigated rock at pressures up to 12 GPa by complementary in-situ diagnostics (X-ray diffraction and falling sphere technic). The obtained solidus and liquidus are well lower (difference >200K), especially at the highest investigated pressures, compared to previous studies, with strong implications for the origin of volcanism and notably the crystallization of the magma ocean. Furthermore, our experiments provide important data to refine the extent of melting (&#934;), modal proportion and the chemistry of all the different phases present between the solidus and the liquidus at different conditions (P, T, &#934;).</p><p>Altogether, these new results are critical to constrain models of thermal evolution and crust extraction and formation, as well as to address the evolution of the magmatism and volcanism at the Mars surface since 3.5 Ga. Finally, depending on different parameters, such as the thickness of the crust or the concentration of radioactive elements, the estimated areotherm could cross the solidus and lead to partial melting of the mantle, especially close to the core-mantle boundary, where a high extent of melting could be reached.</p><div> <div> <div>&#160;</div> </div> </div>
Bulletin of the American Physical Society, Jul 8, 2013
Physical Review E, 2017
We report experimental evidence for a crossover between a liquid-like state and a gas-like state ... more We report experimental evidence for a crossover between a liquid-like state and a gas-like state in fluid methane (CH4). This crossover is observed in all of our experiments, up to 397 K temperature; 2.1 times the critical temperature of methane. The crossover has been characterized with both Raman spectroscopy and X-ray diffraction in a number of separate experiments, and confirmed to be reversible. We associate this crossover with the Frenkel line-a recently hypothesized crossover in dynamic properties of fluids extending to arbitrarily high pressure and temperature, dividing the phase diagram into separate regions where the fluid possesses liquid-like and gas-like properties. On the liquid-like side the Raman-active vibration increases in frequency linearly as pressure is increased, as expected due to the repulsive interaction between adjacent molecules. On the gas-like side this competes with the attractive Van der Waal's potential leading the vibration frequency to decrease as pressure is increased.
2019 IEEE International Conference on Electrical Engineering and Photonics (EExPolytech)
We report the high-temperature and high-pressure single-crystal x-ray diffraction study of PbHfO3... more We report the high-temperature and high-pressure single-crystal x-ray diffraction study of PbHfO3. The increase of pressure enables an additional intermediate phase, located between the cubic and incommensurate phases, and characterized by superstructure reflections indicating the presence of anti-phase oxygen octahedral tilts. The temperature-dependent diffuse peak at an incommensurate position is much better pronounced at higher pressures (~ 2 GPa) than at lower pressures (~ 1.1 GPa), which we interpret as enhancing of the incommensurate soft mode on pressure increase. Several peculiarities in the behavior of superstructural reflections at M- and X- points are reported and discussed.
Physics and Chemistry of Minerals
AGU Fall Meeting Abstracts, Dec 16, 2020
Physics of the Earth and Planetary Interiors, 2017
At higher pressures, the slope of the (Fe,Al)-bearing Bg melting curve remains fairly constant up... more At higher pressures, the slope of the (Fe,Al)-bearing Bg melting curve remains fairly constant up to the CMB pressure of 135 GPa, which contrasts with the flattening reported for MgSiO 3. This makes the different available results to converge to a temperature of 5100-5500 K for the melting of Bg at the CMB. We remind that the melting curve of MgSiO 3-Bg should always plot at higher temperature than that of the (Fe,Al)-bearing composition, due to the incompatible character of Fe and Al. Thus, our experimental determination of the (Fe,Al)-bearing Bg melting curve implies that the melting temperature of MgSiO 3-Bg at very high mantle pressures was underestimated by a couple hundred degrees in some previous studies (de Koker and Stixrude, 2009; Mosenfelder et al., 2009). Thus, for further discussions, we will choose the higher melting curve of MgSiO 3 Bg as determined from ab initio calculations (Stixrude and Karki, 2005). It can be modeled using a modified Simon and Glatzel equation [T=T 0 (P/a + 1) 1 / c ] with parameters T 0 =91 K, a=0.00125 GPa and c=2.83 (Simon and Glatzel, 1929). We note that the liquidus temperature profile reported previously for peridotite (Fiquet et al., 2010) appears superimposed with the melting curve of MgSiO 3-Bg derived from ab initio calculations and shock experiments (Figure 1). This is unexpected because (i) the more complex chemical composition of the Bg phase itself, compared to MgSiO 3 , and (ii) additional Fp and CaSiO 3-perovskite (CaPv) phases should both lower the peridotite liquidus below the melting temperature of pure MgSiO 3. In their study, (Fiquet et al., 2010) observed large crystals of Bg at the center of the heated spot, where the melting behavior was monitored using in situ X-ray diffraction. Chemical composition of Bg grains measured at different locations on a sample synthesized at ~61 GPa show Fe/(Mg+Fe) and Al/Si ratios of ~2.5% and ~8%, respectively. It is possible that their reported measurements of the peridotite liquidus correspond in fact to the melting curve of these large grains of MgSiO 3-bearing Bg. 3.4. VOLUME OF BRIDGMANITE MELTING
AIP Advances, 2016
We report a detailed high pressure study on Eu 1-x Sr x TiO 3 polycrystalline samples using synch... more We report a detailed high pressure study on Eu 1-x Sr x TiO 3 polycrystalline samples using synchrotron x-ray diffraction. We have observed a second-order antiferrodistortive phase transition for all doping levels which corresponds to the transition that has been previously explored as a function of temperature. The analysis of the compression mechanism by calculating the lattice parameters, spontaneous strains and tilt angles of the TiO 6 octahedra leads to a high pressure phase diagram for Eu 1-x Sr x TiO 3 .
Physical Review B, 2015
The structural transformation of multiferroic EuTiO3 has been intensively investigated by synchro... more The structural transformation of multiferroic EuTiO3 has been intensively investigated by synchrotron x-ray diffraction at pressures up to 50.3 GPa and temperatures from 50 to 500 K. An antiferrodistortive phase transition from cubic Pm-3m to tetragonal I4/mcm space group has been observed, identical to the one that has been previously explored at ambient pressure and low temperatures. Several compression/decompression cycles at different temperatures have been carried out to accurately map the transition, and as a result a P-T phase diagram for EuTiO3 has been constructed. The observed phase transition exhibits many similarities with isostructural SrTiO3, although the absence of magnetoelectric interactions in the latter accounts for the different phase boundaries between the two materials.
Physical Review B, 2014
SrMnO 3 is a perovskite compound which, unlike most perovskites, can be synthesized in three diff... more SrMnO 3 is a perovskite compound which, unlike most perovskites, can be synthesized in three different but closely related polymorphs. In this paper, the first experimental equation of state of the 6H polymorphs is reported. The experimentally determined bulk modulus of SrMnO 3 increases from 115.6(11) GPa in the 4H polymorph to 143.7(17) GPa in the 6H polymorph, while DFT calculations predict a further increase to 172.5(4) GPa in the 3C polymorph. The first in situ observations of transformations between the three known polymorphs, under high pressure and high temperature conditions are also reported. The results are compared with extensive DFT calculations and literature, and it is demonstrated that the 6H polymorph is the thermodynamically stable phase between 5.9(3) and 18.1(2) GPa at zero kelvin. The effect of possible oxygen sub-stoichiometry is also explored, used DFT. Finally, the findings are combined with the existing knowledge of the phase behavior in this system to outline where further knowledge needs to be collected before a PT phase diagram can be constructed for this system.
Physica C: Superconductivity and its Applications, 2007
We have studied the effect of aluminum doping and boron isotopic substitution on the Raman spectr... more We have studied the effect of aluminum doping and boron isotopic substitution on the Raman spectra of the Mg 1Àx Al x 10,11 B 2 polycrystalline compounds. Our data show that new peaks appear at 740and870cmAˋ1whilethebroadbandat740 and 870 cm À1 while the broad band at 740and870cmAˋ1whilethebroadbandat600 cm À1 diminishes for higher Al doping levels. The high energy band evolves to the E 2g phonon mode of AlB 2 corresponding to a strong reduction in the electron-phonon coupling. The isotopic shift for the broad band at $600 cm À1 is small considering the isotopic shift of the other bands, which follow the harmonic mass law. This extreme anharmonic behavior indicates that the broad band may not be directly related with the E 2g phonon of the B atoms.
Physica C: Superconductivity and its Applications, 2008
A systematic Raman study has been carried out on single crystals of Mg(B 1Àx C x) 2 with carbon c... more A systematic Raman study has been carried out on single crystals of Mg(B 1Àx C x) 2 with carbon concentrations in the range of x = 0.0-0.15. We have found remarkable differentiations of the Raman spectra with doping. Even with small amounts of carbon substitution (x = 0.027) the E 2g-symmetry broad band at 600cmAˋ1(forpureMgB2)diminishesandnewmodesappearoftheapproximateA1g/B1g(600 cm À1 (for pure MgB 2) diminishes and new modes appear of the approximate A 1g /B 1g (600cmAˋ1(forpureMgB2)diminishesandnewmodesappearoftheapproximateA1g/B1g(750 cm À1) and E 2g ($850 cm À1) symmetries, though the transition temperature is only slightly reduced (<2 K). The broad band does not evolve continuously into the mode of same symmetry at 850cmAˋ1,asassumedbyotherinvestigators.Thepracticaldisappearanceoftheoriginal850 cm À1 , as assumed by other investigators. The practical disappearance of the original 850cmAˋ1,asassumedbyotherinvestigators.Thepracticaldisappearanceoftheoriginal600 cm À1 mode at x ' 0.08 coincides with the fast reduction of T c. The doping dependence of the phonons indicates a two-mode behavior, which could be driven by the 2D-3D electronic topological transition and associated with a possible nanoscale phase separation.
Journal of Physics: Condensed Matter, 2008
A phase separation driven by the negative compressibility of the electron gas, near electronic to... more A phase separation driven by the negative compressibility of the electron gas, near electronic topological transitions (ETT), could drive the system at the verge of a catastrophe. We show here that the metastable phases very close to the ETT transition are observed in a mesoscopic phase separation (MePhS) driven by the quenched lattice disorder. By using high resolution synchrotron radiation x-ray powder diffraction we have identified the MePhS for the intermetallic ternary Mg 1−x Al x B 2 in the proximity of two ETTs: the first at x 1 = 0.1 and the second at x 2 = 0.3. We have identified the competition between a first 'relaxed' (R) hole poor and a second 'tense' (T) hole rich phase, and by micro-Raman we observe the splitting of the in-plane phonon E 2g mode in the proximity of the first ETT at x = 0.1. The anisotropic quenched disorder due to a random distribution of Al 3+ and Mg 2+ ions both in the axial (c axis) direction and planar (ab plane) direction, probed by x-ray diffraction and Raman data, is proposed to be the physical variable that allows the formation of metastable phases near the critical points of electronic topological transitions, where Feshbach shape resonances in interband pairing amplifies the superconducting critical temperature.