{"id":74754,"date":"2018-03-09T23:19:49","date_gmt":"2018-03-09T23:19:49","guid":{"rendered":"https:\/\/www.deberes.net\/tesis\/sin-categoria\/estudio-cristalografico-y-magnetico-de-oxidos-rcro4-rtierra-rara\/"},"modified":"2018-03-09T23:19:49","modified_gmt":"2018-03-09T23:19:49","slug":"estudio-cristalografico-y-magnetico-de-oxidos-rcro4-rtierra-rara","status":"publish","type":"post","link":"https:\/\/www.deberes.net\/tesis\/quimica\/estudio-cristalografico-y-magnetico-de-oxidos-rcro4-rtierra-rara\/","title":{"rendered":"Estudio cristalogr\u00e1fico y magn\u00e9tico de \u00f3xidos rcro4 r=tierra rara"},"content":{"rendered":"<h2>Tesis doctoral de <strong> Enrique Jim\u00e9nez Melero <\/strong><\/h2>\n<p>Durante este trabajo, se ha procedido al estudio tanto cristalogr\u00e1fico como magn\u00e9tico de los \u00f3xidos rcro4 (r = tierra rara). Para ello, se han preparado las muestras mediante el m\u00e9todo de s\u00edntesis consistente en calentar la  mezcla inicial de nitratos en presencia de una corriente de ox\u00edgeno, con el fin de obtener el cromo en el estado de oxidaci\u00f3n 5+. La optimizaci\u00f3n de la temperatura y tiempo de reacci\u00f3n ha permitido la obtenci\u00f3n de los diferentes  compuestos como fases \u00fanicas. Adem\u00e1s, el empleo de un proceso de congelaci\u00f3n o \u00abquenching\u00bb ha dado lugar al el aislamiento por primera vez del polimorfo zirc\u00f3n del prcro4. Sin embargo, la obtenci\u00f3n del polimorfo del prcro4 ha sido posible \u00fanicamente con el empleo altas presiones durante su s\u00edntesis.  la caracterizaci\u00f3n estructural de las muestras as\u00ed obtenidas, ha sido realizada mediante difracci\u00f3n de rayos x y difracci\u00f3n de neutrones a temperatura ambiente. El an\u00e1lisis de los datos ha permitido confirmar la estructura tipo monazita adoptada por el lacro4, mientras que los restantes compuestos rcro4 presentan el tipo estructural zirc\u00f3n. Mediante los experimentos de difracci\u00f3n de neutrones, se han obtenido valores muy precisos  de las coordenadas de los \u00e1tomos de ox\u00edgeno, que ha su vez han constituido la base para la correcta descripci\u00f3n de ambas estructuras, as\u00ed como para la evaluaci\u00f3n de los par\u00e1metros estructurales en funci\u00f3n del i\u00f3n de tierra  rara. Adem\u00e1s, existe en todos estos compuestos una distribuci\u00f3n espacial de microtensiones que resulta ser m\u00e1s acusada a lo largo de la diagonal de la celda unidad tetragonal de alta temperatura. En el caso de los \u00f3xidos  rcro4 (r =nd, tb, tm, yb), se ha observado experimentalmente mediante datos de difracci\u00f3n de neutrones de  alta resoluci\u00f3n la existencia de una distorsi\u00f3n estructural a bajas temperaturas, que conduce a una simetr\u00eda ortorr\u00f3mbica. el grupo espacial que caracteriza a dicha simetr\u00eda es el<\/p>\n<p>&nbsp;<\/p>\n<h3>Datos acad\u00e9micos de la tesis doctoral \u00ab<strong>Estudio cristalogr\u00e1fico y magn\u00e9tico de \u00f3xidos rcro4 r=tierra rara<\/strong>\u00ab<\/h3>\n<ul>\n<li><strong>T\u00edtulo de la tesis:<\/strong>\u00a0 Estudio cristalogr\u00e1fico y magn\u00e9tico de \u00f3xidos rcro4 r=tierra rara <\/li>\n<li><strong>Autor:<\/strong>\u00a0 Enrique Jim\u00e9nez Melero <\/li>\n<li><strong>Universidad:<\/strong>\u00a0 Complutense de Madrid<\/li>\n<li><strong>Fecha de lectura de la tesis:<\/strong>\u00a0 20\/06\/2005<\/li>\n<\/ul>\n<p>&nbsp;<\/p>\n<h3>Direcci\u00f3n y tribunal<\/h3>\n<ul>\n<li><strong>Director de la tesis<\/strong>\n<ul>\n<li>Regino S\u00e1ez Puche<\/li>\n<\/ul>\n<\/li>\n<li><strong>Tribunal<\/strong>\n<ul>\n<li>Presidente del tribunal: Antonio Hernando grande <\/li>\n<li>pierre Bonville (vocal)<\/li>\n<li>paul C.m. gubbens (vocal)<\/li>\n<li>Jos\u00e9 Luis Martinez pe\u00f1a (vocal)<\/li>\n<\/ul>\n<\/li>\n<\/ul>\n<p>&nbsp;<\/p>\n","protected":false},"excerpt":{"rendered":"<p>Tesis doctoral de Enrique Jim\u00e9nez Melero Durante este trabajo, se ha procedido al estudio tanto cristalogr\u00e1fico como magn\u00e9tico de los [&hellip;]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"site-sidebar-layout":"default","site-content-layout":"","ast-site-content-layout":"","site-content-style":"default","site-sidebar-style":"default","ast-global-header-display":"","ast-banner-title-visibility":"","ast-main-header-display":"","ast-hfb-above-header-display":"","ast-hfb-below-header-display":"","ast-hfb-mobile-header-display":"","site-post-title":"","ast-breadcrumbs-content":"","ast-featured-img":"","footer-sml-layout":"","theme-transparent-header-meta":"","adv-header-id-meta":"","stick-header-meta":"","header-above-stick-meta":"","header-main-stick-meta":"","header-below-stick-meta":"","astra-migrate-meta-layouts":"default","ast-page-background-enabled":"default","ast-page-background-meta":{"desktop":{"background-color":"var(--ast-global-color-4)","background-image":"","background-repeat":"repeat","background-position":"center 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