CONTENTS 6524 4.2. Bond-Length Variations 6524 4.3. Bond-Angle Variations 6524 4.4. Variations of the A•••A Distances 6524 5. Concluding Remarks 6524 Author Information 6525 Corresponding Author 6525 Notes 6525 Biographies 6525 Acknowledgments 6526 References 6526

The structure of the fully ordered α-Na(3)Ti(2)(PO(4))(3) NASICON compound was elucidated using high-quality single-crystal data. The cation/vacancy distribution forms a homogeneous 3D arrangement and could represent the absolute cationic ordering available in the full Na(3)M(2)(PO(4))(3) series, as verified for M = Fe. For M = Ti, the reversible α → γ transition was observed at 85 °C, leading to the standard disordered R ̅3c γ model. Through JPDF analysis, the most probable Na(+) zigzag M(2)-M(1) diffusion scheme was directly deduced using our accurate crystallographic data.

Ba2Co2+ 3Co3+ 6O14 has been prepared by conventional solid-state reaction between BaO2 and CoO. Its crystal structure has been refined from single-crystal X-ray diffraction data and powder neutron diffraction, a = 5.6963(8) Å, c = 28.924(6) Å, space group R3̄m, Z = 3, R1 = 4.44%, wR2 = 10.96%. It shows evidence of new building blocks called T‘ (ch‘h‘c stacking sequence of cubic O4 and hexagonal BaO3 layers) by analogy with the related T-blocks (hh‘h‘h) of the barium hexaferrites. T‘ consists of CoII,IIIO2 brucite-like layers pillared by CoIIO4 tetrahedra and CoIII 3O12 octahedral trimers. Below T N = 39 K, tetrahedral and octahedral high spin CoII (S = 3/2) diluted in the framework mainly containing low spin CoIII (S = 0) interact through CoII−O−O−CoII through super-super exchanges (SSE) only. The analysis of the competition between the multiple SSE paths has been performed through geometrical considerations. The magnetic moments are lying antiferromagnetically in the a,b plane in good agreement with the magnetic group theory presented in our work. Their values of 1.70(4) μB and 2.83(3) μB for the octahedral and tetrahedral CoII, respectively, are explained by the high degree of covalency and magnetic transfer toward the surrounding anions involved in the SSEs. At high temperature, the creation of oxygen vacancies is observed and strongly intervenes in the hopping conductivity as shown from the abrupt change in the matching Arrhenius law. This particular feature demonstrates potential mixed conductivity processes in the medium-temperature range. At 1000 °C, it reversibly decomposes into CoO and BaCoO3- δ. Finally, the medium crystallinity of the title compound is explained by the presence of defects and intergrowths with other hexagonal perovskites of the Ba−Co−O system.

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The BiCu(2)(P(1-x)V(x))O(6) system shows the appearance of various phenomena that progressively change as a function of the average (P/V)O(4) groups size. Then, from x = 0 to x approximately 0.7, a solid solution exists with respect to the basic orthorhombic unit cell of BiCu(2)PO(6). For greater x values (0.7 < x <0.96), structural modulations with incommensurate q vector that slightly change versus x appear. The 4-D treatment of single-crystal XRD data of the modulated phase corresponding to x = 0.87 at 100 K (orthorhombic, a = 12.379(3)Angstrom, b = 5.2344(9) Angstrom, c = 7.8270(14) Angstrom, q = 0.268(3) b*, super space group: Xbmm(0gamma0) s00, X stands for the nonprimitive centering vector (1/2,0,1/2,1/2), R(obs)(overall) = 5.27%, R(obs)(fundamental) = 4.48%, R(obs)(satellite) = 6.58%) has evidenced strong positional modulated effects within the [BiCu(2)O(2)](3+) ribbons while three XO(4) configurations compete along the x(4) fourth dimension. There is no P/V segregation along x(4) in good agreement with steric-only origins of the modulation. Finally for 0.96 < x <1, two phases coexist, i.e., BiCu(2)VO(6) (X = 1) and a modulated phase of the previous domain.The BiCu(2)VO(6) crystal structure shows a unit cell tripling associated with monoclinic symmetry lowering. The VO(4) orientations between two ribbons proceed with respect to the interribbon distance. Then the full system shows flexible interactions between modulated Bi/M/O-based ribbons and surrounding tetrahedral groups, depending on the average XO(4) size. Furthermore, between two ribbons the Cu(2+) arrangement forms magnetically isolated zigzag copper two-leg ladders. Our preliminary results show a spin-gap behavior likely due to the existence of true S = (1)/(2) Heisenberg two-leg ladders. Modulated compositions are gapless, in good agreement with band-broadening toward a continuum in the magnetic excitation spectrum. The continuous distribution of Cu-Cu distances along the rungs and legs of the ladders should be mainly responsible for this magnetic change.

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The K-and Na-synthetic analogues of the fumarolic mineral ilinskite have been synthesized by the chemical vapor transport (CVT) reactions method. The A-[Cu 5 O 2 ](SeO 3 ) 2 Cl 3 (A + = K + , Na + ) compounds crystallize in the orthorhombic space group Pnma: a = 18.1691(6) Å, b = 6.4483(2) Å, c = 10.5684(4) Å, V = 1238.19(7) Å 3 , R 1 = 0.018 for 1957 unique reflections with F > 4σ F for K[Cu 5 O 2 ](SeO 3 ) 2 Cl 3 (KI), and a = 17.7489(18) Å, b = 6.4412(6) Å, c = 10.4880(12) Å, V = 1199.0(2) Å 3 , R 1 = 0.049 for 1300 unique reflections with F > 4σ F for Na[Cu 5 O 2 ](SeO 3 ) 2 Cl 3 (NaI). The crystal structures of KI and NaI are based upon the [O 2 Cu 5 ] 6+ sheets consisting of corner-sharing (OCu 4 ) 6+ tetrahedra. The Na-for-K substitution results in the significant expansion of the interlayer space and changes in local coordination of some of the Cu 2+ cations. The A + cation coordination changes from fivefold (for Na + ) to ninefold (for K + ). The CVT reactions method provides a unique opportunity to model physicochemical conditions existing in fumarolic environments and may be used not only to model exhalative processes, but also to predict possible mineral phases that may form in fumaroles. In particular, the K analogue of ilinskite is not known in nature, whereas it may well form from volcanic gases in a K-rich local geochemical environment.