a b s t r a c tDoping of manganese (Mn 3 þ /Mn 4 þ ) into the Aurivillius phase Pb 1 À x Bi 4 þ x Ti 4 À x Mn x O 15 was carried out using the molten salt technique for various Mn concentrations (x ¼0, 0.2, 0.4, 0.6, 0.8, and 1). Single phase samples could be obtained in the composition range with x up to 0.6 as confirmed by X-ray and neutron diffraction analysis. Dielectric measurements show a peak at 801, 803, 813 and 850 K for samples with x ¼0, 0.2, 0.4, and 0.6, respectively, related to the ferroelectric transition temperature (T c ). The main contribution of the in-plane polarization for x r0.2 which was calculated from the atomic positions obtained by the structure analysis is the dipole moment in the Ti(1)O 6 layer; however, for x Z 0.4 the polarization originates from the dipole moment in the Ti(2)O 6 layer. Mn doping in the Pb 1 À x Bi 4 þ x Ti 4 À x Mn x O 15 does not show any long range magnetic ordering.
Apatite-like materials are of considerable interest as potential solid oxide fuel cell electrolytes, although their structural vagaries continue to attract significant discussion. Understanding these features is crucial both to explain the oxide ion conduction process and to optimise it. As the composition of putative P6(3)/m apatites with ideal formula [A(I)(4)][A(II)(6)][(BO(4))(6)][X](2) is varied the [A(I)(4)(BO(4))(6)] framework will flex to better accommodate the [A(II)(6)X(2)] tunnel component through adjustment of the A(I)O(6) metaprism twist angle (varphi). The space group theory prescribes that framework adaptation during phase changes must lead to one of the maximal non-isomorphic subgroups of P6(3)/m (P2(1), P2(1)/m, P1[combining macron]). These adaptations correlate with oxygen ion conduction, and become crucial especially when the tunnels are filled by relatively small ions and/or partially occupied, and if interstitial oxygens are located in the framework. Detecting and completely describing these lower symmetry structures can be challenging, as it is difficult to precisely control apatite stoichiometry and small departures from the hexagonal metric may be near the limits of detection. Using a combination of diffraction and spectroscopic techniques it is shown that lanthanum strontium germanate oxide electrolytes crystallise as triclinic (A), monoclinic (M) and hexagonal (H) bi-layer pseudomorphs with the composition ranges: [La(10-x)Sr(x)][(GeO(4))(5+x/2)(GeO(5))(1-x/2)][O(2)] (0
As part of a study of the long‐term operation of solid‐oxide fuel cells, three (Mn,Co,Cr)3O4 samples have been synthesized and characterized. X‐ray and neutron diffraction patterns from the powder samples at room temperature were measured and the data were co‐refined. The neutron data were indispensible in locating Mn, Co and Cr within the crystallographic unit cell with their respective atomic occupancies. Two of these samples have been identified as cubic Mn0.76Co0.58Cr1.66O4 and Mn1.28Co1.72O4. The third is a two‐phase sample containing cubic Mn1.66Co1.34O4 and tetragonal Mn2.05Co0.91O4 in a 59.1 (6):40.9 (6)% mass fraction ratio. Cr, which might be introduced from reaction with chromia during oxidation of interconnect materials, exhibits a preference for the octahedral site rather than the tetrahedral site. Without Cr, Mn dominates the octahedral site.
We present a precise electric-field-temperature phase diagram of an antiferroelectric liquid crystal with a short pitch Sm-C ␣ * phase. This was obtained by using a photoelastic modulator. A unique field-induced phase was found inside the Sm-C ␣ * phase, which displayed low birefringence. Two tricritical points related to the phase were also observed. In addition, numerical calculations were made based on the discrete phenomenological model. The numerical results reproduced the experimental ones and it was clarified that the phase has a three-layer structure without spatial modulation. Many phases have been found in antiferroelectric smectic liquid crystals. The variety can be ascribed to the interlayer interactions between the tilts of molecules. The Sm-C ␣ * phase with a short pitch helix arises from competition between nearest-neighbor ͑NN͒ and next-nearest-neighbor ͑NNN͒ interactions ͓1͔, and the distorted four-layer phase ͑Sm-C FI2 * ͒ and the distorted three-layer phase ͑Sm-C FI1 * ͒ from NN nonlinear interaction ͓2͔. A phase diagram in a parameter space of coefficients in the free energy was obtained on the basis of a discrete phenomenological model. As the temperature changes, the interactions change so that sequential transitions take place. Consequently, by changing the temperature one can obtain information on the interactions. In addition, using an electric field can also be a good method for investigating the interactions because in chiral smectic liquid crystals the electric field couples with the order parameter representing the amplitude and phase of the molecular tilt in each layer. The electric-field effect has been extensively studied, mainly by using D-E hysteresis loops, optical transmission measurements under ac electric fields, and conoscopic observations ͓3͔. However, these experiments are not detailed enough to precisely detect small orientational changes in molecules over a wide range of temperatures and electric fields.We adopted an optical system using a photoelastic modulator ͑PEM͒, by means of which we could simplify the si-
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