JANA2006 is a freely available program for structure determination of standard, modulated and magnetic samples based on X-ray or neutron single crystal/ powder diffraction or on electron diffraction. The system has been developed for 30 years from specialized tool for refinement of modulated structures to a universal program covering standard as well as advanced crystallography. The aim of this article is to describe the basic features of JANA2006 and explain its scope and philosophy. It will also serve as a basis for future publications detailing tools and methods of JANA.
A new Mo 6 cluster complex and its silica and polyurethane composites have been synthesized and characterized. These materials are highly luminescent with emission above 650 nm, produce singlet oxygen with high efficiency, are photostable, and can be excited up to 580 nm. These proper-[a] Institute of Inorganic Chemistry of the AS CR, v.v.i Husinec-Ř ež 1001, 25068 Ř ež,
We report a new structure determination of the Sr1.2872NiO3 incommensurate composite
hexagonal perovskite compound. Three different refinement strategies are presented: (i) a
3D supercell approximation with a nonharmonic development of the atomic displacement
factor, (ii) an original (3+1)D incommensurate composite description with the use of crenel
functions, and (iii) a (3+1)D commensurate composite model. The three strategies are
discussed and compared to previous refinements carried out for the hexagonal perovskites
in a classical way or with the superspace group formalism. Out of the three methods, the
incommensurate composite approach gives slightly better results with a final global R value
of 2.89% for 635 independent reflections (at a I/σ(I) > 2 level) and only 60 parameters
(R3̄m(00γ)0s superspace group; a = 9.5177(7) Å, c = 2.5739(2) Å, q = 0.64359(4)c*, V =
201.93(4) Å3, and Z = 3). The use of crenel functions notably improves previously reported
results. New structural features are evidenced for Sr1.2872NiO3: (i) an incommensurate
character, (ii) a splitting of the trigonal prismatic nickel atoms over 5 positions, (iii) a definite
stoichiometry which induces a perfect charge balance, and (iv) a nonharmonic behavior of
some Sr atoms. Those characteristics seem general to most hexagonal perovskite compounds
and essential for correctly interpreting their interesting magnetic properties. Finally, a new
generic formulation is proposed, which explains the various stoichiometries observed and
suggests a new compound possibility.
X-ray diffraction, dynamical mechanical analysis and infrared reflectivity
studies revealed an antiferrodistortive phase transition in EuTiO3 ceramics.
Near 300K the perovskite structure changes from cubic Pm-3m to tetragonal
I4/mcm due to antiphase tilting of oxygen octahedra along the c axis (a0a0c- in
Glazer notation). The phase transition is analogous to SrTiO3. However, some
ceramics as well as single crystals of EuTiO3 show different infrared
reflectivity spectra bringing evidence of a different crystal structure. In
such samples electron diffraction revealed an incommensurate tetragonal
structure with modulation wavevector q ~ 0.38 a*. Extra phonons in samples with
modulated structure are activated in the IR spectra due to folding of the
Brillouin zone. We propose that defects like Eu3+ and oxygen vacancies strongly
influence the temperature of the phase transition to antiferrodistortive phase
as well as the tendency to incommensurate modulation in EuTiO3.Comment: PRB, in pres
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