54 research outputs found
Concentration phase diagram of Ba(x)Sr(1-x)TiO3 solid solutions
Method of derivation of phenomenological thermodynamic potential of solid
solutions is proposed in which the interaction of the order parameters of
constituents is introduced through the account of elastic strain due to misfit
of the lattice parameters of the end-members. The validity of the method is
demonstrated for Ba(x)Sr(1-x)TiO3 system being a typical example of
ferroelectric solid solution. Its phase diagram is determined using
experimental data for the coefficients in the phenomenological potentials of
SrTiO3 and BaTiO3. In the phase diagram of the Ba(x)Sr(1-x)TiO3 system for
small Ba concentration, there are a tricritical point and two multiphase points
one of which is associated with up to 6 possible phases.Comment: 8 pages, 3 figure
B-T phase diagram of CoCr2O4 in magnetic fields up to 14 T
We have measured the magnetization and specific heat of multiferroic CoCr2O4
in magnetic fields up to 14 T. The high-field magnetization measurements
indicate a new phase transition at T* = 5 - 6 K. The phase between T* and the
lock-in transition at 15 K is characterized by magnetic irreversibility. At
higher magnetic fields, the irreversibility increases. Specific-heat
measurements confirm the transition at T*, and also show irreversible behavior.
We construct a field-temperature phase diagram of CoCr2O4.Comment: 4 page
Hertz-to-terahertz dielectric response of nanoconfined water molecules
Broad-band dielectric spectroscopy, heat capacity measurements and molecular
dynamic simulations are applied to study excitations of interacting electric
dipoles spatially arranged in a network with an inter-dipole distance of 5-10
A. The dipoles with magnitude of 1.85 Debye are represented by single H2O
molecules located in voids (0.5 nm size) formed by ions of the crystal lattice
of cordierite. We discover emergence of nontrivial disordered paraelectric
phase of dipolar system with signs of phase transition below 3 K.Comment: 3 pages, 4 figure
Origin of Low-Energy Excitations in Charge-Ordered Manganites
The low-energy excitations in the charge-ordered phase of polycrystalline
La0.25Ca0.75MnO3 are explored by frequency-domain terahertz spectroscopy. In
the frequency range from 4 cm^-1 to 700 cm^-1 (energies 0.4 meV to 90 meV) and
at temperatures down to 5 K, we do not detect any feature that can be
associated with the collective response of the spatially modulated charge
continuum. In the antiferromagnetically ordered phase, broad absorption bands
appear in the conductivity and permittivity spectra around 30 cm^-1 and 100
cm^-1 which are assigned to former acoustic phonons optically activated due to
a fourfold superstructure in the crystal lattice. Our results indicate that
characteristic energies of collective excitations of the charge-ordered phase
in La0:25Ca0:75MnO3, if any, lie below 1 meV. At our lowest frequencies of only
few wavenumbers a strong relaxation is observed above 100 K connected to the
formation of the charge-ordered state.Comment: 5 pages, 3 figure
Raman spectroscopic study of the concentration phase trnasition in Pb1 − x CaxTiO3 solid solutions
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