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Centimetre-sized single crystals of high-quality CaBaCo 2 Fe 2 O 7 were synthesized by the optical floating zone technique. The metal-to-metal stoichiometry and oxygen content were confirmed by spectroscopy and thermal reduction experiments. The hexagonal symmetry P6 3 mc (No. 186) well describes the powder X-ray and neutron diffraction as well as single-crystal neutron diffraction at all measured temperatures. This symmetry is also consistent with optical second harmonic generation data obtained between 10 and 295 K. However, a satisfactory structure description from single-crystal neutron diffraction data needs an oxygen split position. Specific heat, magnetic susceptibility and powder neutron diffraction data indicate a magnetic phase transition at T N = 159 K to an antiferromagnetic ground state, but with a persisting hexagonal symmetry and intrinsic geometric frustration.research papers

The hexagonal swedenborgite, CaBaCo 2 Fe 2 O 7 , is a chiral frustrated antiferromagnet, in which magnetic ions form alternating Kagome and triangular layers. We observe a long range √ 3 × √ 3 antiferromagnetic order setting in below TN = 160 K by neutron diffraction on single crystals of CaBaCo 2 Fe 2 O 7 . Both magnetization and polarized neutron single crystal diffraction measurements show that close to TN spins lie predominantly in the ab-plane, while upon cooling the spin structure becomes increasingly canted due to Dzyaloshinskii-Moriya interactions. The ordered structure can be described and refined within the magnetic space group P 31m . Diffuse scattering between the magnetic peaks reveals that the spin order is partial. Monte Carlo simulations based on a Heisenberg model with two nearest-neighbor exchange interactions show a similar diffuse scattering and coexistence of the √ 3 × √ 3 order with disorder. The coexistence can be explained by the freedom to vary spins without affecting the long range order, which gives rise to ground-state degeneracy. Polarization analysis of the magnetic peaks indicates the presence of long-period cycloidal spin correlations resulting from the broken inversion symmetry of the lattice, in agreement with our symmetry analysis.

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Gasification of black liquor is an attractive alternative to the traditional recovery boiler. However, in process modeling of gasification, thermodynamic data for the key components are quite uncertain, which will reduce the reliability of the modeling of the chemical processes in a gasifier. The objective of this work was to experimentally re-determine and improve data on the binary phase diagram Na 2 CO 3 -Na 2 S, especially on the Na 2 CO 3 side of the system, which is the region of interest concerning black liquor combustion and gasification, and also the region with the most significant uncertainties. Measurements were carried out in a dry inert atmosphere at temperatures from 25 to 1200 °C, using high-temperature microscopy (HTM) and hightemperature X-ray powder diffraction (HT-XRD). To examine the influence of pure CO 2 atmosphere on the melting behavior, HTM experiments in the same temperature interval were made. This paper presents new data complementary to earlier published data on the binary phase diagram Na 2 CO 3 -Na 2 S. These include re-determination of liquidus curves, in the Na 2 CO 3 -rich area, melting points of the pure components, as well as determination of the extent of the solid solution, Na 2 CO 3 (ss), area.

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