7,994 research outputs found
A phase-field model of relaxor ferroelectrics based on random field theory
A mechanically coupled phase-field model is proposed for the first time to
simulate the peculiar behavior of relaxor ferroelectrics. Based on the random
field theory for relaxors, local random fields are introduced to characterize
the effect of chemical disorder. This generic model is developed from a
thermodynamic framework and the microforce theory and is implemented by a
nonlinear finite element method. Simulation results show that the model can
reproduce relaxor features, such as domain miniaturization, small remnant
polarization and large piezoelectric response. In particular, the influence of
random field strength on these features are revealed. Simulation results on
domain structure and hysteresis behavior are discussed and compared with
related experimental results.Comment: 8 figure
Electronic structures and magnetic orders of Fe-vacancies ordered ternary iron selenides TlFeSe and AFeSe (A=K, Rb, or Cs)
By the first-principles electronic structure calculations, we find that the
ground state of the Fe-vacancies ordered TlFeSe is a
quasi-two-dimensional collinear antiferromagnetic semiconductor with an energy
gap of 94 meV, in agreement with experimental measurements. This
antiferromagnetic order is driven by the Se-bridged antiferromagnetic
superexchange interactions between Fe moments. Similarly, we find that crystals
AFeSe (A=K, Rb, or Cs) are also antiferromagnetic semiconductors
but with a zero-gap semiconducting state or semimetallic state nearly
degenerated with the ground states. Thus rich physical properties and phase
diagrams are expected.Comment: Add results about AFeSe (A=K, Rb, or Cs);4 pages and 7
figure
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