Y0.76Ho0.24FeGe2O7: a new member of thortveitite-like layered compounds

Y0.76Ho0.24FeGe2O7 (yttrium holmium iron digermanate) was synthesized by solid-state reaction at 1573 K. This thortveitite-like compound presents a crystallographic group–subgroup isotranslational (klassengleiche) relation with some other pyrogermanates, such as FeInGe2O7, In1.08Gd0.92Ge2O7 and InYGe2O7, which are configurationally isotypic with the Sc2Si2O7 thortveitite structure first reported by Zachariasen [(1930 ▶). Z. Kristallogr. 73, 1–6]. Holmium cations share with yttrium the 4f Wyckoff position at the center of a seven-coordinated pentagonal bipyramid, while Fe atoms also occupy one site with Wyckoff position 4f at the center of the octahedron. All these sites have the point symmetry C 1. Two types of Ge2O7 diorthogroups with point symmetry C 1h are present in the structure, each one of them defining a layer type which alternates with the other. These diorthogroups have their tetrahedral groups in an eclipsed conformation

Rietveld refinement of the mixed boracite Fe1.59Zn1.41B7O13Br

The structural characterization of the new iron–zinc hepta­borate bromide with composition Fe1.59Zn1.41B7O13Br, prepared by chemical transport is reported. A rigid-body model with constrained generalized coordinates was defined in order to hold the positions of the B atoms at reasonable inter­atomic distances that typically would reach unacceptable values because of the weak scattering power of boron. There are three independent sites for the B atoms of which two are tetra­hedrally coordinated. The bond-valence sum around the third B atom, located on a threefold rotation axis, was calculated considering two cases of coordination of boron with oxygens: trigonal-planar and tetrahedral. The contribution of the fourth O atom to the bond-valence sum was found to be only 0.06 v.u., indicating the presence of a very weak bond in the right position to have a distorted tetra­hedral coordination in favour of the trigonal-planar coordination for the third B atom. X-ray fluorescence (XRF) was used to determinate the Fe/Zn ratio

Rietveld refinement of Y2GeO5

Y2GeO5 (yttrium germanium penta­oxide) was synthesized by solid-state reaction at 1443 K. The arrangement, which has monoclinic symmetry, is isostructural with Dy2GeO5 and presents two independent sites for the Y atoms. Around these atoms there are distorted six-coordinated YO6 octa­hedra and seven-coordinated YO7 penta­gonal bipyramids. The YO7 polyhedra are linked together, sharing their edges along a surface parallel to ab, forming a sheet. Each of these parallel sheets is inter­connected by means of GeO4 tetra­hedra, sharing an edge (or vertex) on one side and a vertex (or edge) on the other adjacent side. Parallel sheets of YO7 polyhedra are also inter­connected by undulating chains of YO6 octa­hedra along the c axis. These octa­hedra are joined together, sharing a common edge, to form the chain and share edges with the YO7 polyhedra of the sheets

A synchrotron study of Na2.27Ho7.73(SiO4)6O0.72

A well crystallized powder sample of sodium holmium orthosilicate oxyapatite, Na2.27Ho7.73(SiO4)6O0.72, was obtained after mechanical milling and thermal treatment at 1123 K. Crystal structure analysis was performed from the results of Rietveld refinement of the synchrotron diffraction data. As in other rare-earth orthosilicate apatites, sodium cations appear located sharing with holmium the 4f Wyckoff position at the center of a tricapped trigonal prism. In its turn, holmium almost fully occupies the 6h position at the center of a seven-coordinated penta­gonal bipyramid. A small quantity of Na atoms was found at this site. No vacancies are present in the two independent crystallographic sites available for Ho and Na atoms

Comportamiento reproductivo de ovejas F1 (Damara x Merino) sincronizadas con CIDR y dos tiempos de aplicación de GnRH

Este experimento se realizó para evaluar el comportamiento reproductivo en ovejas F1 (Damara x Merino) importadas de Australia, sincronizadas con un dispositivo liberador de la hormona (CIDR) y dos tiempos de aplicación de hormona liberadora de gonadotropinas (GnRH). Cuarenta y cinco ovejas F1 de primer parto con 18.08 ± 0.07 meses de edad y 43.3 ± 5.6 kg de peso corporal, fueron asignadas aleatoriamente a uno de tres tratamientos: T1 (n = 15): CIDR por doce días; T2 (n = 15): CIDR por doce días mas 25 µg de GnRH 48 h antes del retiro del dispositivo y T3 (n = 15): CIDR por doce días mas 25 µg de GnRH al momento del retiro del CIDR. El porcentaje de presentación de estros (100 %) fue similar (p > 0.05) para T1, T2 y T3. El intervalo (h) de inicio del estro sincronizado después del retiro del CIDR fue diferente (p 0.05) para T1, T2 y T3 (60, 53.3 y 46.6 %, respectivamente). La prolificidad promedio general fue de 100.8% y fue similar (p > 0.05) entre tratamientos. La concentración de progesterona determinó que las ovejas probadas tuvieron un cuerpo luteo funcional al comienzo del experimento. Se concluye que el uso combinado de CIDR mas GnRH, 48 h antes y al momento del retiro del dispositivo, no tiene efecto sobre el comportamiento reproductivo en ovejas F1 (Damara x Merino)

Piezoelectric Ceramics of the (1 − x)Bi0.50Na0.50TiO3–xBa0.90Ca0.10TiO3 Lead-Free Solid Solution: Chemical Shift of the Morphotropic Phase Boundary, a Case Study for x = 0.06

Research and development of lead-free piezoelectric materials are still the hottest topics in the field of piezoelectricity. One of the most promising lead-free family of compounds to replace lead zirconate–titanate for actuators is that of Bi0.50Na0.50TiO3 (BNT) based solid solutions. The pseudo-binary (1 − x)Bi0.50Na0.50TiO3–xBa1 − yCayTiO3 system has been proposed for high temperature capacitors and not yet fully explored as piezoelectric material. In this work, the solid solution with x = 0.06 and y = 0.10 was obtained by two different synthesis routes: solid state and Pechini, aiming at using reduced temperatures, both in synthesis (<800 °C) and sintering (<1150 °C), while maintaining appropriated piezoelectric performance. Crystal structure, ceramic grain size, and morphology depend on the synthesis route and were analyzed by X-ray diffraction, together with scanning and transmission electron microscopy. The effects of processing and ceramic microstructure on the structural, dielectric, ferroelectric, and piezoelectric properties were discussed in terms of a shift of the Morphotropic Phase Boundary, chemically induced by the synthesis route

HAp Nanofibers Grown with Crystalline Preferential Orientation and Its Influence in Mechanical Properties of Organic-Inorganic Composite Materials

There are several synthesis techniques to obtain hydroxyapatite (HAp). Some use surfactant agents, amino acids or halogen salts to control structural nucleation and crystal growth. In others, the use of hydrothermal process to carry out the reaction is effective for HAp synthesis. Microwave-assisted hydrothermal method (MAHM) has been successfully applied in the synthesis of HAp nanostructures, which present well-defined morphologies, high crystallinity and high purity. This is important because nano-HAp is attracting interest as a biomaterial for use in prosthetic applications due to its similarity in size, crystallinity and chemical composition with human hard tissue. In this chapter, developments in obtaining HAp nanofibers, with a crystal growth with preferential orientation, as well as morphology control achieved by using the MAHM is discussed. Also, the synthesized fibers were used to cast ceramics with controlled and interconnected porosity through the modified gelcasting process. Then, these HAp ceramics were impregnated with a water solution of gelatin in order to obtain an organic-inorganic composite material, similar to natural bone tissue. The maximum compressive strengths were determined and the composite materials showed mechanical properties that make them suitable to be used as bone tissue implants

Possible Coexistence of Superconductivity and Magnetism in Intermetallic NiBi3

NiBi3 polycrystals were synthesized via a solid state method. X-ray diffraction analysis shows that the main phase present in the sample corresponds to NiBi3 in a weight fraction of 96.82 % according to the refinement of the crystalline structure. SEM - EDS and XPS analysis reveal a homogeneous composition of NiBi3, without Ni traces. The powder superconducting samples were studied by performing magnetic measurements. The superconducting transition temperature and critical magnetic fields were determinated as Tc = 4.05 K, Hc1 = 110 Oe and Hc2 = 3,620 Oe. The superconducting parameters were GL coherence length= 301.5 A, Ginzburg Landau Penetration depth= 1549 A, and k = 5.136. Isothermal measurements below the transition temperature show an anomalous behavior. Above the superconducting transition the compound presents ferromagnetic characteristics up to 750 K, well above the Ni Curie temperature. PACS numbers: Intermetallic Alloys; Superconductivity; Ferromagnetism;Comment: Accepted in Solid State Communication

Interpretación de la varianza fenotípica cuando se consideran efectos genéticos, ambientales e interacción genético ambiental.

En el presente trabajo se discute la importancia que tienen los efectos genéticos producidos por cambios en el medio ambiente y los resultados de la interacción entre estas dos causas de variación. Se hace la especificación matemática de efectos genotípicos ambientales y de la interacción genético-ambiental y se encuentran las ecuaciones con la partición de la varianza fenotípica en sus partes componentes, para diferentes familias formadas en las generaciones subsecuentes al cruzamiento entre dos líneas homocigóticas. ABSTRACT: The genetical effects produced by changes of the environment and the resulting of the interaction between these two sources of variation are discussed in this study. The mathematical specification of the genotypical effects of the environment and the genetic-environmental interaction is found. Also, the equations with the distribution of its components are found for different families formed in the generations after the cross of two homozygotic lines.AGROCIENCIA Vol. 4. Núm. 1. 1969. pp. 29-3