Magnetic interactions in the S = 1/2 square-lattice antiferromagnets Ba2CuTeO6 and Ba2CuWO6: parent phases of a possible spin liquid.

The isostructural double perovskites Ba2CuTeO6 and Ba2CuWO6 are shown by theory and experiment to be frustrated square-lattice antiferromagnets with opposing dominant magnetic interactions. This is driven by differences in orbital hybridisation of Te6+ and W6+. A spin-liquid-like ground state is predicted for Ba2Cu(Te1-xWx)O6 solid solution similar to recent observations in Sr2Cu(Te1-xWx)O6.

Intercalation of Primary Alcohols into Layered Titanoniobates.

Lamellar oxides form an important class of functional materials and are often susceptible to topotactic substitution of the ions between the layers. This opens up the structure to direct reactions with alkylammonium ions often substituting for group 1 ions forcing an increase in layer separation. Proton exchange with group 1 ions is also possible in mineral acids with the resulting protonated materials typically being acidic. These solid acids can further react with bases such as alkyl amines again causing an increase in interlayer separation. Alcohols do not readily form stable ROH2+X- (R alkyl chain, X halide) species and being less basic than RNH2 are less commonly investigated for intercalation into layered oxides. Here the intercalation of simple primary alcohols of the form ROH (R = CxH2x+1; x = 1-10) is investigated using the layered titanoniobate HTiNbO5 as the ceramic host. Direct reaction is found to be ineffective so instead butylamine is first intercalated followed by reaction with the primary alcohols. The butylamine remains in the final product, but intercalation of the alcohols causes a significant modification of the interlayer space of the ceramic. This shows how alcohols can be used to influence the interlayer space of oxide sheets in functional layered oxide ceramics.

Structure and magnetism of the A site scandium perovskite (Sc0.94Mn0.06)Mn0.65Ni0.35O3 synthesized at high pressure.

Scandium perovskite (Sc0.94Mn0.06)Mn0.65Ni0.35O3, synthesized at high pressure and high temperature, has a triclinic structure (space group ) at room temperature and ambient pressure with a √2ap×√2ap×2ap structure with α≈90(°),ß≈89(°),γ≈90(°). Magnetic measurements show that the material displays Curie-Weiss behaviour above 50 K with C=2.11 emu K mol(-1) (µeff=4.11 µB per formula unit) and θ=-95.27 K. Bond valence sum analysis of the crystal structure shows that manganese is present in three different oxidation states (+2, +3, +4), with the +2 oxidation state on the A site resulting in a highly tilted perovskite structure (average tilt 21.2(°) compared with 15.7(°) calculated for LaCaMnNbO6), giving the formula (Sc3+(0.94)Mn2+(0.06))(Mn4+(0.41)Mn3+(0.09))(Mn3+(0.15)Ni2+(0.35))O3.

A polar corundum oxide displaying weak ferromagnetism at room temperature.

Combining long-range magnetic order with polarity in the same structure is a prerequisite for the design of (magnetoelectric) multiferroic materials. There are now several demonstrated strategies to achieve this goal, but retaining magnetic order above room temperature remains a difficult target. Iron oxides in the +3 oxidation state have high magnetic ordering temperatures due to the size of the coupled moments. Here we prepare and characterize ScFeO(3) (SFO), which under pressure and in strain-stabilized thin films adopts a polar variant of the corundum structure, one of the archetypal binary oxide structures. Polar corundum ScFeO(3) has a weak ferromagnetic ground state below 356 K-this is in contrast to the purely antiferromagnetic ground state adopted by the well-studied ferroelectric BiFeO(3).

Microwave plasma synthesis of lanthanide zirconates from microwave transparent oxides.

Lanthanide zirconate phases Ln(2)Zr(2)O(7) and Ln(4)Zr(3)O(12) (Ln = Y, La, Gd, Dy, Ho, Yb) have been prepared using a microwave induced plasma methodology, which allows rapid synthesis using materials which do not couple directly with microwaves at room temperature. We describe the measurement of heating profiles of the precursor binary metal oxides which can be used to identify conditions conducive to the synthesis of more complex oxides. Uncontrolled heating which can be a feature of microwave synthesis of ceramics is not observed, allowing reproducible synthesis. Conventionally these phases are prepared at >1400 °C over hours or days and are being investigated for applications including the immobilisation of nuclear waste where rapid processing is important. Using the microwave plasma method, phase-pure materials have been prepared in minutes. Furthermore, it is clear that Ln(2)Zr(2)O(7) and Ln(4)Zr(3)O(12) also exhibit significant plasma-promoted dielectric heating (e.g. >2200 °C for Dy(4)Zr(3)O(12)) which is typically greater than either of the respective precursors, thus providing a driving force to rapidly complete the reaction.