30 research outputs found
Neutron powder diffraction study of NaMnO and LiMnO: New insights on spin-charge-orbital ordering
The high-pressure synthesized quasi-one-dimensional compounds NaMnO
and LiMnO are both antiferromagnetic insulators, and here
their atomic and magnetic structures were investigated using neutron powder
diffraction. The present crystal structural analyses of NaMn2O4 reveal that
Mn3+/Mn4+ charge-ordering state exist even at low temperature (down to 1.5 K).
It is evident from one of the Mn sites shows a strongly distorted Mn3+
octahedra due to the Jahn-Teller effect. Above TN = 39 K, a two-dimensional
short-range correlation is observed, as indicated by an asymmetric diffuse
scattering. Below TN, two antiferromagnetic transitions are observed (i) a
commensurate long-range Mn3+ spin ordering below 39 K, and (ii) an
incommensurate Mn4+ spin ordering below 10 K. The commensurate magnetic
structure (kC = 0.5, -0.5, 0.5) follows the magnetic anisotropy of the local
easy axes of Mn3+, while the incommensurate one shows a spin-density-wave order
with kIC = (0,0,0.216). For LiMnO, on the other hand, absence
of a long-range spin ordered state down to 1.5 K is confirmed.Comment: 11 pages, 8 figure
Temperature evolution of the crystal structure of Bi1 xPrxFeO3 solid solutions
The crystal structure of solid solutions in the Bi<sub>1 − x</sub> Pr <sub>x</sub> FeO<sub>3</sub> system near the structural transition between the rhombohedral and orthorhombic phases (0.125 ≤ x ≤ 0.15) has been studied. The structural phase transitions induced by changes in the concentration of praseodymium ions and in the temperature have been investigated using X-ray diffraction, transmission electron microscopy, and differential scanning calorimetry. It has been established that the sequence of phase transformations in the crystal structure of Bi<sub>1 − x</sub> Pr <sub>x</sub> FeO<sub>3</sub> solid solutions with variations in the temperature differs significantly from the evolution of the crystal structure of the BiFeO3 compounds with the substitution of other rare-earth elements for bismuth ions. The regions of the existence of the single-phase structural state and regions of the coexistence of the structural phases have been determined in the investigation of the crystal structure of the Bi<sub>1 − x</sub> Pr <sub>x</sub> FeO<sub>3</sub> solid solutions. A three-phase structural state has been revealed for the solid solution with x = 0.125 at temperatures near 400°C. The specific features of the structural phase transitions of the compounds in the vicinity of the morphotropic phase boundary have been determined by analyzing the obtained results. It has been found that the solid solutions based on bismuth ferrite demonstrate a significant improvement in their physical properties