The overall proton conductivity of polycrystalline acceptor-doped BaZrO(3) is limited by the high resistivity of its grain boundaries. To investigate the nature of the electrical response of the grain boundaries as a function of the DC bias, Y-doped BaZrO(3) ceramics with a very large grain size (up to 200 μm) have been prepared in an infrared image furnace. The grains are so large that even individual grain boundaries can be addressed by microelectrodes. DC voltage-dependent resistance and capacitance of the grain boundaries are discussed in terms of the space charge model. The results corroborate carrier depletion (OH(O)˙, h˙, V(O)˙˙) as origin of the pronounced grain boundary resistance. This picture fits well into the space charge scenario found for various related oxide materials, and leads to strategies for improving grain boundary conductivity.

-75 As nuclear magnetic resonance (NMR) experiments were performed on Ba(Fe 1-x Mn x ) 2 As 2 ( x Mn = 2.5%, 5% and 12%) single crystals. The Fe layer magnetic susceptibility far from Mn atoms is probed by the 75 As NMR line shift and is found similar to that of BaFe 2 As 2 , implying that Mn does not induce charge doping. A satellite line associated with the Mn nearest neighbours (n.n.) of 75 As displays a Curie-Weiss shift which demonstrates that Mn carries a local magnetic moment. This is confirmed by the main line broadening typical of a RKKY-like Mn-induced staggered spin polarization. The Mn moment is due to the localization of the additional Mn hole. These findings explain why Mn does not induce superconductivity in the pnictides contrary to other dopants such as Co, Ni, Ru or K. [7]. The resulting phase diagram is very similar in all these cases. It looks as if the only requirement to obtain superconductivity is to destroy sufficiently the antiferromagnetic (AF) state, whatever the mechanism at play.Remarkably, there is an exception to this generic behavior: the substitution of Fe by hole-dopant atoms, namely Cr or Mn. Indeed, Mn and Cr substituted at Fe site do not lead to a superconducting state [8][9][10][11]. Neutron diffraction and magnetotransport measurements reveal that at low concentration, Mn or Cr substitutions reduce the ordering temperature T N by 6 K/% and the ordered moment amplitude remains unaffected [9][10]. Above x = 30% for Cr and x = 12% for Mn, new types of AF states appear whose T N even increases with further substitution. It is a G-type AF ordering for Cr doping [9], whereas Mn doping invokes an unusual tetragonal AF state with no orthorhombic distortion as in the parent compound [10]. Similar qualitative features are also observed in SrFe 2 As 2 with Mn doping [11]. This asymmetry between the effects of hole (Mn, Cr) and electron (Co, Ni) dopants is surprising and still unexplained. The question arises as to why

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We present neutron scattering investigations of the structural dynamical properties of the aperiodic layered compound, Bi2Sr2CaCu2O 8+δ . Acoustic phonons behave identically around the assumed average structure Bragg reflection and around the first satellite. This observation proves that the collective dynamics related to the incommensurate structure are quite different from what is expected in a modulated incommensurate model. Our data indicate two acoustic-like longitudinal branches along the incommensurate direction. Such behavior is compatible with a composite incommensurate structure where these two Bragg peaks correspond to the main reflections of each subsystem.