{"id":3167,"date":"1994-01-01T00:00:00","date_gmt":"1994-01-01T00:00:00","guid":{"rendered":"https:\/\/www.deberes.net\/tesis\/1994\/01\/01\/estudio-de-transiciones-de-fase-en-cristales-ferroelectricos-ferroelasticos-e-inconmensurables-mediante-calorimetria-adiabatica-y-espectroscopia-raman\/"},"modified":"1994-01-01T00:00:00","modified_gmt":"1994-01-01T00:00:00","slug":"estudio-de-transiciones-de-fase-en-cristales-ferroelectricos-ferroelasticos-e-inconmensurables-mediante-calorimetria-adiabatica-y-espectroscopia-raman","status":"publish","type":"post","link":"https:\/\/www.deberes.net\/tesis\/fisica\/estudio-de-transiciones-de-fase-en-cristales-ferroelectricos-ferroelasticos-e-inconmensurables-mediante-calorimetria-adiabatica-y-espectroscopia-raman\/","title":{"rendered":"Estudio de transiciones de fase en cristales ferroelectricos, ferroelasticos e inconmensurables mediante calorimetria adiabatica y espectroscopia raman."},"content":{"rendered":"<h2>Tesis doctoral de <strong>  Igartua Aldamiz Josu Mirena <\/strong><\/h2>\n<p>El trabajo que se presenta constituye una contribucion al estudio sobre transiciones de fase en solidos con caracter ferroelectrico, ferroelastico e inconmensurable.  se han utilizado diversas tecnicas experimentales, en funcion de la informacion requerida por cada cristal. Sin embargo, el peso experimental ha recaido fundamentalmente sobre dos: la calorimetria adiabatica y la espectroscopia raman. Entre las restantes tecnicas utilizadas citaremos la difraccion de rayos x, tanto sobre monocristal como en polvo cristalino, observaciones opticas, medidas dielectricas y calorimetria diferencial de barrido.  en las transiciones de tipo inconmensurable el cristal pierde su periodicidad espacial por congelacion de un modo de vibracion cuyo periodo espacial no es conmensurable con las constantes de la red. Entre los numerosos cristales que presentan este tipo de fases se encuentran los pertenecientes a la fase a2bx4, donde a=monovalente nh4, n(ch3)4, b=zn,co,mn, etc y x=halogeno.  por lo que se refiere a los derivados clorados de tetrametilamonio (n(ch3)4)2mc14, la mayoria de ellos presentan una complicada secuencia de transiciones por debajo de la temperatura ambiente, que incluye fases ferroelectricas, ferroelasticas e inconmensurables. El presente trabajo aborda el estudio de esta familia de compuestos con el fin de aclarar la influencia del halogeno en la secuencia de transiciones de fase. Para ello se han estudiado los derivados: (n(ch3)4)2znbr4 y (n(ch3)4)2zni4. De la misma manera, dentro de los cristales con grupos tetrametilamonio, se encuentra la familia de compuestos de la forma n(ch3)4mx3( m: metal bivalente, x:halogeno). Como contribucion inicial a una investigacion calorimetrica sistematica de los cristales de esta familia, se presenta un estudio del n(ch3)4cdbr3 y de transicion de fase ferro-paraelectrica que presenta a 161k.  entre los numerosos cristales que muestran fases inconmensurables fuera de las familias anteri<\/p>\n<p>&nbsp;<\/p>\n<h3>Datos acad\u00e9micos de la tesis doctoral \u00ab<strong>Estudio de transiciones de fase en cristales ferroelectricos, ferroelasticos e inconmensurables mediante calorimetria adiabatica y espectroscopia raman.<\/strong>\u00ab<\/h3>\n<ul>\n<li><strong>T\u00edtulo de la tesis:<\/strong>\u00a0 Estudio de transiciones de fase en cristales ferroelectricos, ferroelasticos e inconmensurables mediante calorimetria adiabatica y espectroscopia raman. <\/li>\n<li><strong>Autor:<\/strong>\u00a0  Igartua Aldamiz Josu Mirena <\/li>\n<li><strong>Universidad:<\/strong>\u00a0 Pa\u00eds vasco\/euskal herriko unibertsitatea<\/li>\n<li><strong>Fecha de lectura de la tesis:<\/strong>\u00a0 01\/01\/1994<\/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>Angel Lopez Echarri<\/li>\n<\/ul>\n<\/li>\n<li><strong>Tribunal<\/strong>\n<ul>\n<li>Presidente del tribunal: Manuel Jose Tello Leon <\/li>\n<li>Michel Couzi (vocal)<\/li>\n<li>Domingo Gonzalez Alvarez (vocal)<\/li>\n<li>Honza Arend (vocal)<\/li>\n<\/ul>\n<\/li>\n<\/ul>\n<p>&nbsp;<\/p>\n","protected":false},"excerpt":{"rendered":"<p>Tesis doctoral de Igartua Aldamiz Josu Mirena El trabajo que se presenta constituye una contribucion al estudio sobre transiciones de [&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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