Sr Analogue Research Articles

Synthesis, Structure, and Properties of A14AlSb 11 ( A = Ca, Sr, Ba)

A 14AlSb 11 ( A = Ca, Sr, Ba) is synthesized by reacting the elements in stoichiometric amounts at high temperature (1250°C). Single-crystal X-ray diffraction data (130 K: a = 17.493 (4) Å, c = 23.480 (8) Å (Sr); a = 18.293 (2) Å, c = 24.222 (9) Å (Ba)) were refined (tetragonal, I4 1/ acd (142), Z = 8; R = 4.02%, R w = 4.26% (Sr); R = 3.71%, R w = 4.34% (Ba)) and showed these compounds to be isostructural to Ca 14AlSb 11. Single-crystal X-ray and microprobe data indicate that these compounds are slightly deficient in Al. Temperature-dependent resistivity measurements show that these materials are intrinsic semiconductors with activation energies of 0.0143, 0.0667, and 0.4814 eV for the Ca, Sr, and Ba analogs, respectively.

The 57Fe Mössbauer spectra of oriented single-crystal and powder PbFe12O19 (abstract)

The recent determination of the crystal structure of PbFe12O19 by means of single-crystal x-ray diffraction has made it possible to carry out a definitive and comparative analysis of the structure-property relationship of PbFe12O19, SrFe12O19, and BaFe12O19. We have therefore performed 57Fe Mössbauer measurements on oriented, single-crystal, and powder samples of PbFe12O19 at 298 K. For a single-crystal oriented parallel to the c axis, five distinct patterns are observed. The hyperfine fields, isomer shifts, and quadrupole interactions are as follows: 12k: Heff=413 kOe; δ=0.33 mm s−1; Δ=0.35 mm s−1; 4f1: 487 kOe; 0.24 mm s−1; 0.13 mm s−1; 4f2: 514 kOe; 0.39 mm s−1; 0.29 mm s−1; 2a: 496 kOe; 0.30 mm s−1; 0.11 mm s−1; 2b: 399 kOe; 0.30 mm s−1; 2.00 mm s−1. The relative magnitude of each of these parameters is in good agreement with and exhibits the same trend observed for high-purity SrFe12O19. The relative intensity of the 2b pattern for the crystal oriented parallel to the c axis is 8.2%, which approaches its theoretical value; of the total number of iron ions in the structure, 8.33% of them occupy the 2b site. The value for the polycrystalline sample is only 5.4% of the total intensity. However, for a single crystal oriented perpendicular to the c axis, the 2b pattern exhibits a negligible intensity within the experimental error. This result confirms the dynamic disorder in the position of the 2b iron ions and suggests a stronger anisotropy for the case of PbFe12O19 than for SrFe12O19 and BaFe12O19. Even though the trend in hyperfine parameters at 298 K is similar to Sr, Ba, and Pb hexaferrites, PbFe12O19 exhibits hyperfine fields that are consistently lower than those of the Ba and Sr analogues. This result is discussed in terms of the Curie temperatures, magnetic exchange interactions, and structural parameters.

Complexes of the lanthanide(III) ions with an aromatic six-nitrogen-donor macrocyclic ligand

A series of complexes of formula ML 3 X 3 •nS, in which M is La(III)-Yb(III), L 3 is C 26 H 18 N 6 , X is a mononegative ion, and S is water or methanol, were obtained by metal-templated condensation from 2,6-diformylpyridine and 1,2-diaminobenzene, as well as by metal exchange from Ba(L 3 ) 2 (ClO 4 ) 2 . The spectral properties of the complexes (IR and 1 H and 13 C NMR spectra for the diamagnetic species) closely resembled those of the Sr(II) analogue, the structure of which was established by X-ray analysis

Metal ion binding by amino acids. Preparation and crystal structures of magnesium, strontium, and barium L‐glutamate hydrates

AbstractCrystalline magnesium, strontium, and barium L‐glutamate complexes containing the dianion L‐Glu2− have been prepared as the tetrahydrate (Mg) and hexahydrates (Sr, Ba), respectively. Their aqueous solutions have pH values of 10.45, 11.05, and 10.93, respectively. The solid state structures of the Mg and Sr complexes have been determined by single crystal X‐ray methods, and the structure of the Ba analogue inferred through its isomorphism with the Sr analogue. The crystals are orthorhombic, space group P212121. The magnesium atoms were found to be hexacoordinated with the L‐glutamate functioning as a chelating N,Oα‐donor. Four water molecules complete the first coordination sphere. The γ‐carboxylate group is only engaged in hydrogen bonding. Strontium and barium are nine‐coordinated. The α‐carboxylate group of the L‐Glu2− ligand is O,O‐chelating to one metal and forming oxygen bridges to two further metal atoms. The γ‐carboxylate group is also chelating a neighbouring strontium atom, but the nitrogen function is not engaged in metal coordination. By MOM bridging double strings of metal‐oxygen chains are formed, which are interlinked by the amino acids to give a layered structure. Three water molecules are also part of the first coordination sphere of each metal, while three others are interlayer hydrogen‐bonded components. The amino groups are also involved in this hydrogen bonding.

High-pressure, synthetic loveringite-davidite and its rare earth element geochemistry

AbstractLoveringite-davidite members of the crichtonite group were synthesized at high pressure and temperature (7.5 kbar, 1000–1050 °C) from a melt of TiO2 and rare earth element (REE) enriched basaltic andesite composition. Four sets of partition coefficients for La, Srn, Ho, Lu and Sr (analogue for Eu2+) were obtained. These show that light and heavy REE are readily accommodated, but the intermediate REE are discriminated against in the loveringite—davidite structure. This confirms the previously proposed two sites (A and M) for REE substitution in the crichtonite group. Additional experiments verified the stability of REE-rich crichtonite group minerals to 20 kbar, 1300 °C and 30 kbar, 1000 °C, and indicate that this phase may be an important accessory repository for the light and heavy REE in the upper mantle.

Luminescence and Structural Properties of Thiogallate Phosphors Ce+3 and Eu+2‐Activated Phosphors. Part I

Thiogallate compounds represented by the formula were prepared by solid‐state reaction. Single crystals of the alkaline earth derivatives were also obtained by vapor transport of the corresponding polycrystalline material. X‐ray diffraction analyses of the single crystals show that is cubic belonging to space group while and are isomorphous belonging to the orthorhombic space group . X‐ray powder diffraction results on the other derivatives indicate that they are all isostructural with the Sr analogue. The alkaline earth thiogallates are the basis of a new type of sulfide phosphor. Rare earth ions readily substitute for the alkaline earth in the host lattice resulting in phosphors that fluoresce strongly under ultraviolet and cathode rays. The luminescence properties of the host compounds and the Ce+3 and Eu+2‐Activated phosphors are described.