Synthesis, X-Ray Diffraction (XRD), Differential Thermal Analysis (DTA), and Scanning Electron Microscopy (SEM) of the Alloy (CuInTe2)1-x(NbTe)x with x=0.5

A polycrystalline ingot (30mm long, 10mm diameter) of the alloy (CuInTe2)1-x(NbTe)x with x=0.5 has been produced using the melt and anneal technique and characterized by X-Ray Diffraction (XRD), Diferential Thermal Analysys (DTA) and Scanning Electron Microscopy (SEM). From XRD results, and using Rietveld refinement method, the crystal structure has been obtained indicating than this alloy crystallizes in a chalcopyrite-like structure, space group  (Nº 112), unit cell parameters a = 6.1933(2) Å, c = 12.4293(2) Å, V = 476.75(2) Å3, figures of merit Rexp= 6.7%, Rp= 7.5%, Rwp= 7.3%, and S = 1.1. DTA measurements indicate three thermal transitions at 1028, 977 and 886 K in the heating cycle, and 1016, 900 and 848 K in the cooling. The transitions at 1028 and 1016 correspond to the melting and solidification point, respectively; the transitions at 977 and 900 K are of solid to liquid+solid type, whereas the transitions at 886 and 848 K correspond to order-disorder. The melting point is incongruent. In the diffraction pattern, traces of a secondary phase are observed; this phase has been identified using SEM technique as (CuIn)0.5NbTe2. DOI: http://dx.doi.org/10.17807/orbital.v14i1.167

Synthesis, X-Ray Diffraction (XRD), Differential Thermal Analysis (DTA), and Scanning Electron Microscopy (SEM) of the Alloy (CuInTe2)1-x(NbTe)x with x=0.5

A polycrystalline ingot (30mm long, 10mm diameter) of the alloy (CuInTe2)1-x(NbTe)x with x=0.5 has been produced using the melt and anneal technique and characterized by X-Ray Diffraction (XRD), Diferential Thermal Analysys (DTA) and Scanning Electron Microscopy (SEM). From XRD results, and using Rietveld refinement method, the crystal structure has been obtained indicating than this alloy crystallizes in a chalcopyrite-like structure, space group  (Nº 112), unit cell parameters a = 6.1933(2) Å, c = 12.4293(2) Å, V = 476.75(2) Å3, figures of merit Rexp= 6.7%, Rp= 7.5%, Rwp= 7.3%, and S = 1.1. DTA measurements indicate three thermal transitions at 1028, 977 and 886 K in the heating cycle, and 1016, 900 and 848 K in the cooling. The transitions at 1028 and 1016 correspond to the melting and solidification point, respectively; the transitions at 977 and 900 K are of solid to liquid+solid type, whereas the transitions at 886 and 848 K correspond to order-disorder. The melting point is incongruent. In the diffraction pattern, traces of a secondary phase are observed; this phase has been identified using SEM technique as (CuIn)0.5NbTe2. DOI: http://dx.doi.org/10.17807/orbital.v14i1.167

Preparation, Crystal Structure, Thermal Analysis, Scanning Electron Microscopy and Optical Band-Gaps of Cu2GeTe4 and Cu2SnTe4 Alloys

Polycrystalline samples (weight ~ 1g) of Cu 2 GeTe 4 and Cu 2 SnTe 4 alloys were prepared by the usual melt and anneal method and the products characterized by X-Ray Diffraction (XRD), Differential Thermal Analysis (DTA), Scanning Electron Microscopy (SEM) and Optical Diffuse Reflectance UV / VIS / NIR Spectroscopytechniques. It was found that: a) Cu 2 GeTe 4 and Cu 2 SnTe 4 crystallize in an orthorhombic structure (sg Imm2; N o44) with lattice parameters a = 5.9281 (4) Å, b = 4.2211 (6) Å, c = 12.645 (5) Å and a = 6.0375 (6) Å, b = 4.2706 (3) Å, c = 12.844 (1 ) Å, respectively; b) both alloys show two thermal transitions: 762 and 636K upon heating and; 700 and 578K upon cooling for Cu 2 GeTe 4 ; 702 and 636K upon heating and; 650 and 590K upon cooling for Cu 2 SnTe 4 ; c) both alloys present large deviations of stoichiometry for the cations Cu (~ 35%), Ge (7.2%) and Sn (26.4%) and minor deviation within the experimental error, for the anion Te; and, d) the measured optical band gaps were 0.63 and 0.53 eV for Cu 2 SnTe 4 and Cu 2 GeTe 4 , respectively.Polycrystalline samples (weight ~ 1 g) of the Cu 2 GeTe 4 and Cu 2 SnTe 4 alloys were prepared by the melting and annealing method and the products characterized by the techniques of X-ray diffraction (XRD), Thermal Differential Analysis (ATD). ), Scanning Electron Microscopy (SEM) and UV / VIS / CIR diffuse optical reflectance spectroscopy. It was found that: a) Cu 2 GeTe 4 and Cu 2 SnTe 4 crystallize in an orthorhombic structure (ge Imm2; N o44) with network parameters a = 5.9281 (4) Å, b = 4.2211 (6) Å, c = 12.645 (5) Å and a = 6.0375 (6) Å, b = 4.2706 (3) Å, c = 12.844 (1) Å, respectively; b) both alloys show two thermal transitions: 762 and 636K when heating and; 700 and 578K after cooling for Cu 2 GeTe 4 ; 702 and 636K when heating and; 650 and 590K after cooling for Cu 2 SnTe 4 ; c) both alloys present important stoichiometric deviations in their cations: Cu (~ 35%), Ge (7.2%) and Sn (26.4%) and lower than the experimental error for the anion Te; and d) the optical energy gaps measured were 0.63 and 0.53 eV for Cu 2 SnTe 4 and Cu 2 GeTe 4, respectively

Estructura cristalina del nuevo semiconductor cuaternario CuVInSe₃

La estructura cristalina del compuesto cuaternario CuVInSe₃ que pertenece al sistema (CuInSe₂)₁‑ₓ (VSe)ₓ con x = 0.5, se analizó usando datos de difracción de rayos X en muestras policristalinas. Este material cristaliza en el grupo espacial tetragonal, P42c (Nº 112), con parámetros de celda unidad a= 5.7909(4) ų, c = 11.625 (1)4, V= 389.84(5) Å3. El refinamiento Rietveld de 25 variables instrumentales y estructurales condujo a los factores de confiabilidad Rexp = 6.6%, Rp = 8. 7%, Rwp = 8.8% y S = 1.3 para 4501 intensidades y 153 reflexiones independientes. Este compuesto tiene una estructura de tipo adamantano normal y es isoestructural con el cuaternario CuFeInSe₃The crystal structure of the quaternary compound CuVInSe₃ belonging to the system (CuInSe₃)₁‑ₓ (VSe)ₓ with x= 0.5, was analyzed using X-ray powder diffraction data. This material crystallizes in the tetragonal space group P42c (Nº 112), with unit cell parameters a= 5.7909(4) Å, e= 11.625(1)Å,V= 389.84(5)Á3. The Rietveld refinementof25 instrumental and structural variables led to R = 6.6 %, R = 8.7 %, R = 8.8 % and exp p wp S = 1.3 for 4501 step intensities and 153 independent reflections. This compound has a normal adamantane structure and is isostructural with CuFelnSe₃

Scutoids are a geometrical solution to three-dimensional packing of epithelia

As animals develop, tissue bending contributes to shape the organs into complex three-dimensional structures. However, the architecture and packing of curved epithelia remains largely unknown. Here we show by means of mathematical modelling that cells in bent epithelia can undergo intercalations along the apico-basal axis. This phenomenon forces cells to have different neighbours in their basal and apical surfaces. As a consequence, epithelial cells adopt a novel shape that we term “scutoid”. The detailed analysis of diverse tissues confirms that generation of apico-basal intercalations between cells is a common feature during morphogenesis. Using biophysical arguments, we propose that scutoids make possible the minimization of the tissue energy and stabilize three-dimensional packing. Hence, we conclude that scutoids are one of nature's solutions to achieve epithelial bending. Our findings pave the way to understand the three-dimensional organization of epithelial organs.España Ministerio de Ciencia y Tecnología BFU2013-48988-C2-1-P and BFU2016-8079

Síntesis y caracterización de las aleaciones cuaternarias CuTaAlSe3 Y CuTaGaSe3

The ingots of CuTaAlSe3 and CuTaGaSe3 were synthesized using the melt and annealing technique. X-Ray Diffraction (XRD) and Differential Thermal Analysis (DTA) techniques were used for characterization of the alloy. The analysis of the diffraction pattern indicates that both samples are composed by two phases; the mean phase indexes as a hexagonal structure, whereas the secondary phase indexes as a tetragonal chalcopyrite-like structure. From the shape of the DTA peaks for the CuTaAlSe3 and CuTaGaSe3 alloys, was deduced that the melting is incongruent for both materials, value of ~1348K and ~1235K, respectively.  Los lingotes de CuTaAlSe3 y CuTaGaSe3 se sintetizaron usando la técnica de fusión y recocido. Se usaron técnicas de difracción de Rayos X (DRX) y Análisis Térmico Diferencial (ATD) para la caracterización de las aleaciones. El análisis del patrón de difracción, indica que ambas muestras están compuestas por dos fases; la fase promedio indexada como una estructura Hexagonal, mientras que la fase secundaria indexa como una estructura tetragonal de tipo calcopirita. De la forma de los picos del ATD para las aleaciones CuTaAlSe3 y CuTaGaSe3, se deduce que la fusión es incongruente para ambos materiales, de valor aproximado 1348K y 1235K, respectivamente

Información Investigador: Grima Gallardo, Pedro José Domingo

Doctorado0264II - 2002115 - 2005; 85 - 2003; 85 - 2001Física; Ciencias de los Materiales; Altas Presiones y Altas Temperaturas.Noviembre de 2005Lic. en Física+58 274 2401332Facultad de [email protected]

El eje del mal en Mérida.

CONTENIDO Sección Documentos ¿Qué significa la transformación de la ULA?Los organismos de co-gobierno y autoridades. Ramírez I., Lílido N. Propuestas generales para la transformación de la Universidad de Los Andes. Ramírez I., Lílido N. Becas estudiantiles integrales y dignas para los estudiantes de la ULA. Ramírez I., Lílido N. Sección Formación de Recursos Humanos Comunicación 3 de becarios en Europa al CU-ULA Sección Sección Presupuesto Universitario El eje del mal en Mérida. Grima, Pedro Sección Elecciones Universitarias Inscripción del equipo rectoral bolivariano. Propuestas para el rectorado. Rodríguez, Alfonso Propuestas para la secretaría. Briceño Méndez, Manuel Sección Ideología La nueva universidad. Márquez P., Jairo Sección Relación Docente / Alumno Revisión crítica de la docencia superior. Zuleta R., Eduardo [email protected] analíticotrimestra