Frustrated magnetic lattices offer the possibility of many exotic ground states that are of great fundamental importance. Of particular significance is the hunt for frustrated spin-1/2 networks as candidates for quantum spin liquids, which would have exciting and unusual magnetic properties at low temperatures. The few reported candidate materials have all been based on d(9) ions. Here, we report the ionothermal synthesis of [NH(4)](2)[C(7)H(14)N][V(7)O(6)F(18)], an inorganic-organic hybrid solid that contains a S = 1/2 kagome network of d(1) V(4+) ions. The compound exhibits a high degree of magnetic frustration, with significant antiferromagnetic interactions but no long-range magnetic order or spin-freezing above 2 K, and appears to be an excellent candidate for realizing a quantum spin liquid ground state in a spin-1/2 kagome network.

Alternative descriptions for the ground state structure of the half-doped manganite Pr 0.5 Ca 0.5 MnO 3 have been tested against high-resolution 10 K x-ray and neutron powder diffraction data. The best fit is obtained using a P2 1 / m symmetry model, which supports the striped charge and orbital ordering picture. The magnitude of the charge ordering is, however, only 25% of the ideal Mn 3+ /Mn 4+ separation. An alternative Pnm2 1 pseudosymmetry, used to describe Zener polaron ordering in Pr 0.6 Ca 0.4 MnO 3 [Phys. Rev. Lett. 89, 097205 (2002)], gives a different, bistriped, charge and orbitally ordered model that does not fit the data as well.

The layered perovskite CsBiNb 2 O 7 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 °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 polarizationselectric 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 CsBiNb 2 O 7 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 µS cm -1 at 250 °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.