Browsing by Autor "Jennifer A. Aitken"

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ALEACIONES DE (CuAlSe2)1-X (TaSe)X (0 ≤ X ≤ 0.5): MEDIDAS DE DIFFRACCION DE RAYOS X, CALORIMETRIA DIFERENCIAL DE BARRIDO Y MICROSCOPIA ELECTRONICA DE BARRRIDO
(2021) P. Grima; Marcos Muñoz; Sonia Durán; Gerzón E. Delgado; Eduardo Pérez Cappe; Jennifer A. Aitken; Dibya Prakash Ray
Polycrystalline samples belonging to the (CuAlSe2)1-x (TaSe)x alloys system, in the composition interval 0 ≤ x ≤ 0.5, were synthesized by the melt and anneal method. X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM), and Differential Thermal Analysis (DTA) techniques were used for the characterization of the products. From XRD it can be observed a chalcopyrite-like single phase in the composition range 0≤ x ≤0.1, with lattice parameters very close to CuAlSe2 and two-phases, chalcopyrite-like and hexagonal-Cu0.52TaSe2, for 0.1 < x ≤ 0.5. By SEM, the stoichiometry for all samples had been measured and the new phase was identified as (Cu0.4Al0.3)TaSe2 . From DTA the respective phase transitions with temperature were obtained. Using the experimental information, a preliminary T-x phase diagram was proposed.
COEXISTENCE OF SUPERPARAMAGNETIC AND FERROMAGNETIC COMPONENTS IN (CuGa) 1-x Fe x Se 2-x SOLID SOLUTIONS WITH x=0.1, 1/3 and 1/2 ( COEXISTENCIA DE COMPONENTES FERROMAGNÉTICA Y SUPERPARAMAGNÉTICA EN SOLUCIONES SÓLIDAS (CUGA) 1-X FE X SE 2-X CON X=0.1, 1/3 Y 1/2 )
(2018) P. Grima; Luis Nieves; Miguel Angel Alfaro Soto; Miguel Quintero; Humberto Cabrera; Inti Zumeta‐Dubé; Alejandro Rodríguez; Jennifer A. Aitken; P. Raics
The magnetic behavior of (CuGa) 1-x Fe x Se 2-x solid solutions with compositions x=0.1, 1/3 and 1/2 has been investigated using SQUID techniques. DC magnetic susceptibility was measured in the temperature range 2 < T < 300K using Zero Field Cooling (ZFC) – Field Cooling (FC) protocol. It has been observed that the experimental curves can be analyzed as the sum of two magnetic components, one superparamagnetic and the other one ferromagnetic. The ferromagnetic component persist up to temperatures higher than room temperature making this report the first observation of room temperature ferromagnetism in A I B III C VI 2 compounds doped (or alloyed)with transition metals. El comportamiento magnetico de las soluciones solidas (CuGa) 1-x Fe x Se 2-x con composiciones x=0.1, 1/3 y 1/2 fue investigado por medio de la tecnica de SQUID. Las susceptibilidades DC fueron medidas en el rango de temperatura 2 < T < 300K usando el protocolo Enfriamiento a Campo Zero (ECZ) – Enfriamiento con Campo (EC). Se observo que las curvas experimentales podian ser analizadas como la suma de dos componentes magneticas, una superparamagnetica y otra ferromagnetica. La componente ferromagnetica persiste a temperaturas por arriba de la temperatura ambiente siendo este reporte la primera observacion de ferromagnetismo a temperatura ambiente en compuestos A I B III C VI 2 dopados (o aleados) con metales de transicion.
PHASE DIAGRAM OF (CuInTe 2 ) 1-x (FeTe) x ALLOYS (0 ≤ x ≤ 0.6) ( DIAGRAMA DE FASES DEL SISTEMA DE ALEACIONES (CuInTe 2 ) 1-x (FeTe) x (0 ≤ x ≤ 0.6)
(2017) P. Grima; M. Quintero; Luis Nieves; Humberto Cabrera; Eduardo Pérez Cappe; Inti Zumeta‐Dubé; Jennifer A. Aitken; Jacilynn A. Brant
Polycrystalline samples of the (CuInTe2)1-x (FeTe)x alloy system where prepared by the melt and anneal technique and the products characterized by X-Ray Diffraction (XRD), Differential Thermal Analysis (DTA) and Optical Diffuse Reflectance Spectroscopy (ODRS) techniques. A first sight, samples were composed by a tetragonal phase with traces of a secondary phase identified as Fe1.125Te. Under exhaustive examination, it was found that the tetragonal phase, at the same time, is composed by two phases, with the same crystal structure and close lattice parameters, typical of spinodal decomposition. From ODRS measurements, optical absorption vs energy curves was obtained. These curves show how the addition of Fe produces a disordering-reordering process in the cationic sublattice suggesting that composition x=0.5 (CuFeInTe3) could be an intermediate compound in the diagram. Using the obtained information, a preliminary T-x phase diagram is proposed. Se prepararon muestras policristalinas del sistema de aleaciones (CuInTe2)1-x (FeTe)x por la tecnica de fusion y recocido; los productos fueron caracterizados por las tecnicas de Difraccion de Rayos X (DRX), Analisis Termico Diferencial (ATD) y Reflectancia por Espectroscopia de Optica Difusa (REOD). A primera vista, las muestras se componen de una fase tetragonal con trazas de una fase secundaria identificada como Fe1.125Te. Bajo un examen mas exhaustivo, se encontro que la fase tetragonal se compone a su vez de dos fases, con la misma estructura cristalina y parametros de red cercanos, tipico de una descomposicion espinodal. A partir de mediciones REOD, se obtuvieron las curvas de absorcion optica vs energia. Estas curvas muestran como la adicion de Fe produce un proceso de desorden-reorden en la subred cationica que sugiere que la composicion x = 0,5 (CuFeInTe3) podria ser un compuesto intermediario en el diagrama. Con la informacion obtenida, se propone un diagrama de fases T-x.
PREPARATION, CRYSTAL STRUCTURE, THERMAL ANALYSIS, SCANNING ELECTRON MICROSCOPY AND OPTICAL BAND-GAPS OF Cu 2 GeTe 4 AND Cu 2 SnTe 4 ALLOYS ( PREPARACION, ESTRUCTURA CRISTALINA, ANALISIS TERMICO, MICROSCOPIA ELECTRONICA DE BARRIDO Y BRECHA OPTICA DE ENERGIA DE LAS ALEACIONES Cu 2 GeTe 4 Y Cu 2 SnTe 4 )
(2015) P. Grima; Ricardo Peña; Luis Nieves; G. Marcano; Miguel Quintero; Ekadink Moreno; Jacilynn A. Brant; Jennifer A. Aitken
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 Spectroscopy techniques. It was found that: a) Cu 2 GeTe 4 and Cu 2 SnTe 4 crystallize in an orthorhombic structure (s.g. Imm2; N o 44) with lattice parameters a=5.9281(4) A, b=4.2211(6) A, c=12.645(5) A and a=6.0375(6) A, b= 4.2706 (3) A, c=12.844(1) A, 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. Se prepararon muestras policristalinas (peso ~ 1 g) de las aleaciones Cu 2 GeTe 4 y Cu 2 SnTe 4 por el metodo de fusion y recocido y los productos caracterizados por las tecnicas de Difraccion de Rayos X (DRX ) , Analisis Termico Diferencial (ATD), Microscopia Electronica de Barrido (MEB) y espectroscopia de reflectancia optica difusa UV / VIS / CIR. Se encontro que : a) Cu 2 GeTe 4 y Cu 2 SnTe 4 cristalizan en una estructura ortorrombica ( g.e. Imm2; N o 44 ) con parametros de red a = 5,9281 (4) A , b = 4.2211 (6) A , c = 12.645 (5) A y a = 6.0375 (6) A , b = 4,2706 (3) A , c = 12.844 (1) A , respectivamente ; b) ambas aleaciones muestran dos transiciones termicas : 762 y 636K al calentar y ; 700 y 578K tras el enfriamiento para Cu 2 GeTe 4 ; 702 y 636K al calentar y ; 650 y 590K tras el enfriamiento para Cu 2 SnTe 4 ; c) ambas aleaciones presentan importantes desviaciones estequiometricas en sus cationes: Cu (~35%), Ge (7.2%) and Sn (26.4%) y menor que el error experimental para el anion Te; y d) las brechas opticas de energia medidas fueron 0.63 y 0.53 eV para Cu 2 SnTe 4 y Cu 2 GeTe 4 , respectivamente.
Synthesis, X-ray diffraction and Magnetic measurements of Cu (Ni, Co) In S4 alloys: Superconductor behavior of CuCo2InS4
(2020) P. Grima; Gerzon Delgado; Eduardo Pérez Cappe; Jennifer A. Aitken; Dibya Prakash
Polycrystalline samples of CuCo2InS4 and CuNi2InS4 alloys were prepared by the melt and anneal method. The products were characterized by X-Ray Diffraction (XRD) and Superconducting Quantum Interference Device (SQUID) techniques. From XRD it was found that both alloys, CuCo2InS4 and CuNi2InS4, are composed by two orthorhombic phases. In the case of CuCo2InS4, the crystal structure of the main phase has been refining (Rietveld method) as Pmn21 (N 31) with lattice parameters a=8.100(1) A, b=7.116(8) A and c=6.391(6) A; for CuNi2InS4, the lattice parameters of the two phases were indexed (DICVOL 06). With respect to the magnetic behavior, CuCo2InS4 is a superconductor with Tc=3.2 K whereas CuNi2InS4 is a high temperature (Tc ~ 380 K) weak ferromagnetic with abnormal temperature dependence of the coercitive field.