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HfMnSb2 is synthesized by solid state reaction of stoichiometric mixtures of the elements (pressed pellet, evacuated quartz tube, 800 °C, 48 h).

K3Fe6F19 is synthesized from a stoichiometric mixture of KF, FeF2, and FeF3 (Ag tube, N2, 550—650 °C, 12 h) and characterized by single crystal XRD, powder neutron diffraction, and magnetic measurements.

The crystal structure and magnetic properties of the RbMnPO4 zeolite-ABW-type material have been studied by temperature-dependent neutron powder diffraction, low-temperature magnetometry, and heat capacity measurements. RbMnPO4 represents a rare example of a weak ferromagnetic polar material, containing Mn(2+) ions with TN = 4.7 K. The neutron powder diffraction pattern recorded at T = 10 K shows that the compound crystallizes in the chiral and polar monoclinic space group P2(1) (No. 4) with the unit cell parameters: a = 8.94635(9), b = 5.43415(5), and c = 9.10250(8) A and β = 90.4209(6)°. A close inspection of the crystal structure of RbMnPO4 shows that this material presents two different types of zigzag chains running along the b axis. This is a unique feature among the zeolite-ABW-type materials exhibiting the P2(1) symmetry. At low temperature, RbMnPO4 exhibits a canted antiferromagnetic structure characterized by the propagation vector k1 = 0, resulting in the magnetic symmetry P2(1)'. The magnetic moments lie mostly along the b axis with the ferromagnetic component being in the ac plane. Due to the geometrical frustration present in this system, an intermediate phase appears within the temperature range 4.7-5.1 K characterized by the propagation vector k2 = (kx, 0, kz) with kx/kz ≈ 2. This ratio is reminiscent of the multiferroic phase of the orthorhombic RMnO3 phases (R = rare earth), suggesting that RbMnPO4 could present some multiferroic properties at low temperature. Our density functional calculations confirm the presence of magnetic frustration, which explains this intermediate incommensurate phase. Taking into account the strongest magnetic interactions, we are able to reproduce the magnetic structure observed experimentally at low temperature.

Stoichiometric quantities of T′-La2CuO4 are obtained by reaction of T-La2CuO4 with CaH2 at 200 °C for two days leading to La2CuO3.5 which is subsequently reoxidized at 300 °C in air.

One of the key points of interest in pyrochlore materials containing bismuth derives from the dielectric properties of some such materials that are linked to the displacements of the bismuth atoms from the ideal site. This study uses high pressure to probe the variations in, and causes of, these displacements. Under compression Bi2Ti2O7 does not undergo any phase changes, but Bi2Sn2O7 undergoes a similar series of changes to those observed during heating. The trigonal β-Bi2Sn2O7 structure is solved from high temperature powder neutron diffraction data and hence the sequence of phases observed in Bi2Sn2O7 is discussed for the first time. The variation in Bi displacements can be considered in terms of the frustration of the tetrahedral lattice that accommodates them. It can also be inferred that the main driver for Bi displacement is a deficiency in the bond valence sum of bismuth.

Ba2NF (I), Ba2NCl (II), Ba2NCl0.8Br0.2 (III), Ba2NCl0.6Br0.4 (IV), Ba2NCl0.4Br0.6 (V), Ba2NCl0.2Br0.8 (VI), Ba2NBr (VII), and Ba2NBr0.8I0.2 (VIII) are prepared by reaction of the respective barium halides BaX2 (X: F, Cl, Br, I) with Ba2N (998 K, 5 d).

In 1949 Shull et al. [1] used for the first time neutrons for the determination of a magnetic structure. Ever since, the need for neutrons for the study of magnetism has increased. Two main reasons can be brought forward to explain this ongoing success: First of all a strong rise in research on functional materials (founding obliges) and secondly the increasing availability of easy to use programmes for the treatment of magnetic neutron diffraction data. The giant magnetoresistance effect, multiferroic materials, magnetoelasticity, magnetic shape memory alloys, magnetocaloric materials, high temperature superconductivity or spin polarized half metals: The last 15 years have seen the event of all these “hot topics” where the knowledge of the magnetism is a prerequisite for understanding the underlying functional mechanisms. Refinement programs like FULLPROF or GSAS and programs for magnetic symmetry analysis like BASIREPS or SARAH make the determination of magnetic structures accessible for non specialists. Following a historical overview on the use of neutron powder diffraction for the determination of magnetic structures, I will try to convince you of the easiness of using magnetic symmetry analysis for the determination of magnetic structures using some recent examples of own research on the rare earth iron borate TbFe3(BO3)4 and the rare earth transition metal telluride Ho6FeTe2.

We report the synthesis of the new compounds R15Si9C with R = Sm, Gd–Er, Y and R15Ge9C with R = Ce, Pr and Nd. These compounds crystallize in the hexagonal La15Ge9Fe structure type (hP50, P63mc, Z = 2) which is an ordered superstructure of La5Ge3 (Mn5Si3-type, hP16, P63/mcm, Z = 2). The superstructure is absent in a single-phase R5Ge3C0.33 alloy with R = Sm and Gd. The addition of interstitial carbon modifies the magnetic properties significantly as regards the magnetic transition temperature and the nature of the magnetic ordering. Carbon doping induces mostly a ferromagnetic or ferrimagnetic configuration. The preponderance of ferromagnetic interactions in the superstructure compounds, with respect to the parent phases, can tentatively be attributed to a change in the sign of the RKKY interactions. The dense Kondo lattice state of Ce in ferrimagnetic Ce5Ge3 is preserved in Ce15Ge9C. Large coercive fields (∼4–5 kOe) at low temperatures are observed in most compounds, which exceed ∼50 kOe in the two Sm based compound.

A series of sulfides NiCr2-xVxS4 (0 < x < 2.0) has been synthesized at high temperatures. All products are isostructural with Cr3S4 (space group I2/m; a ≈ 5.9 A, b ≈ 3.4 A, c ≈11.1 A; β ≈ 91.8°) in...

A new series of non-stoichiometric sulfides Ga1−xGexV4S8−δ (0≤x≤1; δ≤0.23) has been synthesized at high temperatures by heating stoichiometric mixtures of the elements in sealed quartz tubes. The samples have been characterized by powder X-ray diffraction, SQUID magnetometry and electrical transport-property measurements. Structural analysis reveals that a solid solution is formed throughout this composition range, whilst thermogravimetric data reveal sulfur deficiency of up to 2.9% in the quaternary phases. Magnetic measurements suggest that the ferromagnetic behavior of the end-member phase GaV4S8 is retained at x≤0.7; samples in this composition range showing a marked increase in magnetization at low temperatures. By contrast Ga0.25Ge0.75V4S8−δ appears to undergo antiferromagnetic ordering at ca. 15 K. All materials with x≠1 are n-type semiconductors whose resistivity falls by almost six orders of magnitude with decreasing Ga content, whilst the end-member phase GeV4S8−δ is a p-type semiconductor. The results demonstrate that the physical properties are determined principally by the degree of electron filling of narrow-band states arising from intracluster V–V interactions.

The layered perovskite CsBiNb2O7 has been reinvestigated in the light of recent predictions of ferroelectric behavior. Variable temperature powder neutron diffraction experiments show that this material retains polar symmetry (space group P2(1)am) up to at least 900 degrees C, with only a slight decrease in net polarization up to this temperature, calculated using a simple ionic model. However, ac impedance measurements show only a modest dielectric constant (19-27) throughout the temperature range studied. Moreover, convincing evidence for ferroelectric behavior in polarization-electric field loops could not be obtained because of overriding electrical conductivity. Further measurements of electrical behavior, at different temperatures and under both "wet" and "dry" atmospheres, provide clear evidence that CsBiNb2O7 is hygroscopic, with water uptake resulting in significant protonic conductivity. Even in the "dehydrated" state the material is a semiconductor with a modest conductivity of 3.8 mu S cm(-1) at 250 degrees C. Although ferroelectric behavior is not observed in the samples studied here, we cannot rule out the possibility that ferroelectricity might be obtained in samples processed under appropriate conditions.

Conventional high-temperature reactions limit the control of coordination polyhedra in transition-metal oxides to those obtainable within the bounds of known coordination geometries for a given transition metal. For example, iron atoms are almost exclusively coordinated by three-dimensional polyhedra such as tetrahedra and octahedra. However, recent works have shown that binary metal hydrides act as reducing agents at low temperatures, allowing access to unprecedented structures. Here we show the reaction of a perovskite SrFeO3 with CaH2 to yield SrFeO2, a new compound bearing a square-planar oxygen coordination around Fe2+. SrFeO2 is isostructural with 'infinite layer' cupric oxides, and exhibits a magnetic order far above room temperature in spite of the two-dimensional structure, indicating strong in-layer magnetic interactions due to strong Fe d to O p hybridization. Surprisingly, SrFeO2 remains free from the structural instability that might well be expected at low temperatures owing to twofold orbital degeneracy in the Fe2+ ground state with D(4h) point symmetry. The reduction and the oxidation between SrFeO2 and SrFeO3 proceed via the brownmillerite-type intermediate SrFeO2.5, and start at the relatively low temperature of approximately 400 K, making the material appealing for a variety of applications, including oxygen ion conduction, oxygen gas absorption and catalysis.