Recent advancements on the structural evolution of orthorhombic perovskites at high-pressure highlight that perovskites having cations with same formal valence at both cubic and octahedral site (i.e. 3:3) define different compressional patterns when transition metal ions (TMI) are involved. Besides to verify the common paradigm for which the evolution of orthorhombic perovskites with P defines dichotomous trends depending on the formal charge of A and B cations (and thus depending on the relative compressibility of the cubic and octahedral sites), it is shown that perovskites 3:3 bearing TMI define a distinct pattern. The aim of our proposal is to investigate at HP two sets of perovskite compounds (i.e. belonging to the Y(Al1‒xCrx)O3 and to the Nd(Ga1‒xCrx)O3 solid solutions ,respectively) previously characterized at ambient conditions through structural refinements and electronic absorption spectroscopy. This investigation will provide a deeper comprehension on the reciprocal role of the constituting cations. Indeed, while octahedral cations of the Y(Al1–xCrx)O3 join are characterized by a sensible ionic radius difference (i.e. 0.525 and 0.615 Å for Al3+ and Cr3+, respectively), those of the Nd(Ga1‒xCrx)O3 system are, from a steric point of view, almost identical. Octahedrally coordinated Cr3+ and Ga3+ have approximately the same ionic radius (i.e. 0.615 and 0.62 Å, respectively) and very similar dipole polarizability (1.45 Å3 and 1.50 Å3, respectively). On the other hand, Cr3+ is a transition metal ion with partially filled 3d orbitals and strong crystal field stabilization energy at octahedral sites, whereas Ga3+ (full 3d orbitals) as well as Al3+ exhibit no crystal field effects. The effects induced by the TMI at HP regimes will be extremely useful to outline a more accurate compressional model of orthorhombic perovskites for the deep Earth’s mantle as well as to thoroughly understand the role of the crystal field on the compressibility of minerals.
Effect of transition metal ions on the compressibility of orthorhombic perovskites
ARDIT, Matteo;CRUCIANI, Giuseppe
2015
Abstract
Recent advancements on the structural evolution of orthorhombic perovskites at high-pressure highlight that perovskites having cations with same formal valence at both cubic and octahedral site (i.e. 3:3) define different compressional patterns when transition metal ions (TMI) are involved. Besides to verify the common paradigm for which the evolution of orthorhombic perovskites with P defines dichotomous trends depending on the formal charge of A and B cations (and thus depending on the relative compressibility of the cubic and octahedral sites), it is shown that perovskites 3:3 bearing TMI define a distinct pattern. The aim of our proposal is to investigate at HP two sets of perovskite compounds (i.e. belonging to the Y(Al1‒xCrx)O3 and to the Nd(Ga1‒xCrx)O3 solid solutions ,respectively) previously characterized at ambient conditions through structural refinements and electronic absorption spectroscopy. This investigation will provide a deeper comprehension on the reciprocal role of the constituting cations. Indeed, while octahedral cations of the Y(Al1–xCrx)O3 join are characterized by a sensible ionic radius difference (i.e. 0.525 and 0.615 Å for Al3+ and Cr3+, respectively), those of the Nd(Ga1‒xCrx)O3 system are, from a steric point of view, almost identical. Octahedrally coordinated Cr3+ and Ga3+ have approximately the same ionic radius (i.e. 0.615 and 0.62 Å, respectively) and very similar dipole polarizability (1.45 Å3 and 1.50 Å3, respectively). On the other hand, Cr3+ is a transition metal ion with partially filled 3d orbitals and strong crystal field stabilization energy at octahedral sites, whereas Ga3+ (full 3d orbitals) as well as Al3+ exhibit no crystal field effects. The effects induced by the TMI at HP regimes will be extremely useful to outline a more accurate compressional model of orthorhombic perovskites for the deep Earth’s mantle as well as to thoroughly understand the role of the crystal field on the compressibility of minerals.I documenti in SFERA sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
