Manganese oxides with perovskite structure form solid solutions of the type: (MeMnO3)x(ReMnO3)1-x, in which trivalent rare earth ions (Re = La, Pr, Y ….) are progressively substituted with divalent metal ions (Me = Ca, Ba, Sr …). This substitution produces a mixed-valence state of Mn3+ and Mn4+ ions giving rise to a phase diagram rich in interesting transitions and phenomena such as metal to insulator transition (MI), magnetoresistance (MR) and charge ordering (CO) effects. Some of these oxides, in a range of composition, exhibit colossal magnetoresistance effect (CMR) that renewed intense attention on these materials. The special features of manganese oxide perovskites originate from a delicate balance among structural, magnetic and electronic degrees of freedom whose main ingredients are: the double exchange (DE) and super-exchange (SE) interactions between Mn ions, plus the coupling between charge carriers and lattice distortions driven by the Jahn-Teller effect on Mn3+ ions.Relevant information on the physics of these materials can be derived from studies under high pressure since squeezing the structure is a way to alter the scale of the interactions involved. In this work the structure of La1-xCaxMnO3 solid solutions (x=0, 0.25, 0.50, 0.67, 1) under high pressure (up to 40-45 GPa) has been investigated by synchrotron X-ray powder diffraction (XRD). The volume vs. pressure (P-V) equation of state is reported as a function of composition providing a complete description of this interesting class of systems. All the members of the solid solution except the extreme compounds: LaMnO3 and CaMnO3, present low-pressure orthorhombic (Pnma) phase evolving toward and high-pressure tetragonal (I 4/mcm) symmetry. The details of this transition are related to the Ca doping: on increasing the Ca content, the critical pressure of the transition decreases, but the energetic cost of the transition increases. This study depicts a peculiar evolution of structural distortions as a function of pressure and concentration.
Meneghini, C., Mobilio, S., Sani, A., Manju, U., Sarma, D. (2004). EXPLORING THE HIGH PRESSURE PHASE DIAGRAM OF La1-xCaxMnO3.
EXPLORING THE HIGH PRESSURE PHASE DIAGRAM OF La1-xCaxMnO3
MENEGHINI, CARLO;MOBILIO, Settimio;
2004-01-01
Abstract
Manganese oxides with perovskite structure form solid solutions of the type: (MeMnO3)x(ReMnO3)1-x, in which trivalent rare earth ions (Re = La, Pr, Y ….) are progressively substituted with divalent metal ions (Me = Ca, Ba, Sr …). This substitution produces a mixed-valence state of Mn3+ and Mn4+ ions giving rise to a phase diagram rich in interesting transitions and phenomena such as metal to insulator transition (MI), magnetoresistance (MR) and charge ordering (CO) effects. Some of these oxides, in a range of composition, exhibit colossal magnetoresistance effect (CMR) that renewed intense attention on these materials. The special features of manganese oxide perovskites originate from a delicate balance among structural, magnetic and electronic degrees of freedom whose main ingredients are: the double exchange (DE) and super-exchange (SE) interactions between Mn ions, plus the coupling between charge carriers and lattice distortions driven by the Jahn-Teller effect on Mn3+ ions.Relevant information on the physics of these materials can be derived from studies under high pressure since squeezing the structure is a way to alter the scale of the interactions involved. In this work the structure of La1-xCaxMnO3 solid solutions (x=0, 0.25, 0.50, 0.67, 1) under high pressure (up to 40-45 GPa) has been investigated by synchrotron X-ray powder diffraction (XRD). The volume vs. pressure (P-V) equation of state is reported as a function of composition providing a complete description of this interesting class of systems. All the members of the solid solution except the extreme compounds: LaMnO3 and CaMnO3, present low-pressure orthorhombic (Pnma) phase evolving toward and high-pressure tetragonal (I 4/mcm) symmetry. The details of this transition are related to the Ca doping: on increasing the Ca content, the critical pressure of the transition decreases, but the energetic cost of the transition increases. This study depicts a peculiar evolution of structural distortions as a function of pressure and concentration.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
