Polymeric aqua(glutarato)(hydrogen glutarato)lanthanum(III) monohydrate

The structure of the title compound, [La(C5H6O4)(C5H7O4)(H2O)] . H2O, consists of dense layers formed by chains of one-edge-sharing LaO9 (H2O) polyhedra, linked together by the glutarate ligand. The three-dimensional polymeric structure, built up through connection of these layers by the hydrogen glutarate ligand, exhibits cavities accommodating a guest water molecule. The lanthanum ion is tenfold coordinated by four glutarates, acting as bridging-chelating carboxylate groups, by three hydrogen glutarates, three times monodentate, and by one water molecule. Its coordination polyhedron is highly distorted and intermediate between a bicapped dodecahedron and a tetracapped trigonal prism. Hydrogen bonding links the two water molecules and the framework built up from this polynuclear coordination polymer. A very short hydrogen bond, D ... A = 2.484 (3) Angstrom, links the protonated with the deprotonated acid groups in the hydrogen glutarate. [References: 12] 1

Study of new relaxor materials in BaTiO3BaZrO3La2/3TiO3 system

Dielectric studies were performed on new lead-free ceramics derived from BaTiO3 by iso-valent and off-valent substitutions in both octahedral and dodecahedral sites and having the compositions (Ba1−xLa2x/3)(Ti1−yZry)O3, with 0 < x < 0.35 and 0 < y < 0.35. The dielectric permittivities of samples measured as a function of temperature and frequency showed relaxor or classical transition phase. The classical ferroelectric behaviour is exhibited by compositions close to the binary systems BaTiO3–La2/3TiO3 (BT–LT) or BaTiO3–BaZrO3 (BT–BZ), as long as the substitution rates remained small (x <0.15 and y <0.30). The relaxor behaviour occurred in compositions BT–LT, BT–BZ and BT–LT–BZ which deviated strongly from BaTiO3. The values of peak temperature TC (or Tm) decreased with increasing x and/or y, being less sensitive to y variations than that of x. In the relaxor zone, the decreasing of Tm is accompanied with an increasing of the characteristic ΔTm, in BT–LT (x < 0.15) and BT–LT–BZ (x = 0.10; 0.05 < y < 0.35) solid solutions. For the best relaxor material of composition (Ba0.90La0.2/3)(Ti0.95Zr0.05)O3, the dielectric constant (ε'r ) and the peak temperature Tm exhibited interesting values (22 000 and 200 K, respectively) if compared to other similar perovskite-like materials. Moreover, such ceramics are lead-free and could fit to environmental friendly requirements in the case of applications

Study of new relaxor materials in BaTiO3BaZrO3La2/3TiO3 system

Dielectric studies were performed on new lead-free ceramics derived from BaTiO3 by iso-valent and off-valent substitutions in both octahedral and dodecahedral sites and having the compositions (Ba1−xLa2x/3)(Ti1−yZry)O3, with 0 < x < 0.35 and 0 < y < 0.35. The dielectric permittivities of samples measured as a function of temperature and frequency showed relaxor or classical transition phase. The classical ferroelectric behaviour is exhibited by compositions close to the binary systems BaTiO3–La2/3TiO3 (BT–LT) or BaTiO3–BaZrO3 (BT–BZ), as long as the substitution rates remained small (x <0.15 and y <0.30). The relaxor behaviour occurred in compositions BT–LT, BT–BZ and BT–LT–BZ which deviated strongly from BaTiO3. The values of peak temperature TC (or Tm) decreased with increasing x and/or y, being less sensitive to y variations than that of x. In the relaxor zone, the decreasing of Tm is accompanied with an increasing of the characteristic ΔTm, in BT–LT (x < 0.15) and BT–LT–BZ (x = 0.10; 0.05 < y < 0.35) solid solutions. For the best relaxor material of composition (Ba0.90La0.2/3)(Ti0.95Zr0.05)O3, the dielectric constant (ε'r ) and the peak temperature Tm exhibited interesting values (22 000 and 200 K, respectively) if compared to other similar perovskite-like materials. Moreover, such ceramics are lead-free and could fit to environmental friendly requirements in the case of applications

Ferroelectric relaxor behaviour of Ba1-xAx(Ti0.7Zr0.3)O3 and Ba1-xA'2x/3 x/3(Ti0.7Zr0.3)O3 compositions (A = Ca, Sr ; A' = Y, La, Bi)

In order to investigate the effect of A-site homovalent and heterovalent substitution on phase transition in barium titanium zirconium oxide (Ba(Ti0.7Zr0.3)O3), dielectric studies were performed on ceramics of Ba1−xAx(Ti0.7Zr0.3)O3 and Ba1-xA'2x/3 x/3(Ti0.7Zr0.3)O3 compositions (A=Ca, Sr; A′=Y, La, Bi). A preliminary X-ray powder diffraction study has allowed us to determine the limits of solid solution for each composition. A relaxor behaviour appears whatever the value of x in the solid solution domains. The corresponding relaxor characteristics were determined and discussed according to the substituted cation in the twelve coordination number (12-C.N.) crystallographic site. Such new materials are of interest for environmental-friendly applications

Studies of two lanthanide coordination polymers built up from dinuclear units

International audienceThe two three-dimensional oxo-bridged lanthanides \[Ln(2) (C4H2O4)(3) (H2O)(4)]center dot 3H(2)O\(3)(proportional to), with Ln=Ho3+ (1); Gd3+ (2), are isomorphous. They have layer-type structures built up from non-centrosymmetric dinuclear unit Ln(2)O(12)(H2O)(4), beside three lattice H2O molecules stabilizing the 3D open-framework. The building entities are linked through one classical syn-anti mu 2-carboxylato-(KO)-O-1:(KO)-O-1' bridge. Within the bi-polyhedra, two double mu 2-O';(KO)-O-2,O' bridges and a syn-syn classical one, support the magnetic measurements carried out on holmium compound indicating relatively weak anti-ferromagnetic interactions. The comparison with magnetic studies on the almost similar reported Gd(III) compound, suggested that concomitant antiferromagnetic and ferromagnetic properties could not be excluded. The two distinct thermal behaviors evidenced the higher metal-water bond strength with the smaller cation, and revealed the great supramolecular effects generated by hydrogen-bonding patterns