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Two B-site ordered double perovskites, La 2 LiReO 6 and Ba 2 YReO 6 , with S = 1 were investigated as geometrically frustrated antiferromagnets, using x-ray and neutron diffraction, superconducting quantum interference device magnetometry, heat capacity, muon spin relaxation ͑SR͒, and 89 Y magic-angle spinning ͑MAS͒ NMR. La 2 LiReO 6 has a monoclinic structure ͑P2 1 / n͒ with cell parameters at room temperature; a = 5.58262͑22͒ Å, b = 5.67582͑20͒ Å, c = 7.88586͑27͒ Å, and ␤ = 90.240͑4͒°. A zero-field cooled/field cooled ͑ZFC/FC͒ divergence at 50 K was observed in the susceptibility. The ZFC susceptibility is zero below ϳ5 K for polycrystalline samples, suggesting a cooperative singlet ground state but weak moments are induced by cooling in very small fields ϳ1 mT. No evidence of long-range ordering is evident in heat capacity, neutrondiffraction, or SR data. The ZF spin dynamics from SR are anomalous and can be fitted to a stretched exponential rather than the Kubo-Toyabe form expected for random frozen spins but the muon spins are decoupled in longitudinal fields ͑LF͒, consistent with spin freezing of the fraction of spins relaxing within the muon time scale. The internal fields sensed by the muons are anomalously small, consistent with an electronic spin-singlet state. Ba 2 YReO 6 is found to be cubic ͑Fm3m͒ with cell parameter a = 8.36278͑2͒ Å at 300 K with no change in symmetry at 3.8 K, at variance with the Jahn-Teller theorem for a t 2g 2 configuration for Re 5+ . 89 Y MAS NMR shows a single peak indicating that Y/Re site disorder is at most 0.5%. The susceptibility shows two broad peaks around 50 and 25 K but no evidence for long-range order from heat capacity, neutron diffraction, or SR. The ZF SR result shows a two-component ground state with both slow and fast relaxations and decoupling results in a 1 kG LF, indicating spin freezing. These results are in sharp contrast to the long-range AF order found in the S =3/ 2 isostructural materials, La 2 LiRuO 6 and Ba 2 YRuO 6 , indicating that the reduction to S = 1 plays a major role in ground state determination.

The International Union of Crystallography (IUCr) Commission on Powder Diffraction (CPD) has sponsored a round robin on the determination of quantitative phase abundance from diffraction data. Specifically, the aims of the round robin were (i) to document the methods and strategies commonly employed in quantitative phase analysis (QPA), especially those involving powder diffraction, (ii) to assess levels of accuracy, precision and lower limits of detection, (iii) to identify specific problem areas and develop practical solutions, (iv) to formulate recommended procedures for QPA using diffraction data, and (v) to create a standard set of samples for future reference. Some of the analytical issues which have been addressed include (a) the type of analysis (integrated intensities or full‐profile, Rietveld or full‐profile, database of observed patterns) and (b) the type of instrument used, including geometry and radiation (X‐ray, neutron or synchrotron). While the samples used in the round robin covered a wide range of analytical complexity, this paper reports the results for only the sample 1 mixtures. Sample 1 is a simple three‐phase system prepared with eight different compositions covering a wide range of abundance for each phase. The component phases were chosen to minimize sample‐related problems, such as the degree of crystallinity, preferred orientation and microabsorption. However, these were still issues that needed to be addressed by the analysts. The results returned indicate a great deal of variation in the ability of the participating laboratories to perform QPA of this simple three‐component system. These differences result from such problems as (i) use of unsuitable reference intensity ratios, (ii) errors in whole‐pattern refinement software operation and in interpretation of results, (iii) operator errors in the use of the Rietveld method, often arising from a lack of crystallographic understanding, and (iv) application of excessive microabsorption correction. Another major area for concern is the calculation of errors in phase abundance determination, with wide variations in reported values between participants. Few details of methodology used to derive these errors were supplied and many participants provided no measure of error at all.

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Here we report the synthesis and basic characterization of LaFe 1-x Co x AsO for several values of x. The parent phase LaFeAsO orders antiferromagnetically (T N  145 K). Replacing Fe with Co is expected to both electron dope the system and introduce disorder in the FeAs layer. For x = 0.05 antiferromagnetic order is destroyed and superconductivity is observed at T c onset = 11.2 K. For x = 0.11 superconductivity is observed at T c onset = 14.3 K, and for x = 0.15 T c onset = 6.0 K. Superconductivity is not observed for x = 0.2 and 0.5, but for x = 1, the material appears to be ferromagnetic (T c  56 K) as judged by magnetization measurements. We conclude that Co is an effective dopant to induce superconductivity. Somewhat surprisingly, the system appears to tolerate considerable disorder in the FeAs planes.