Chalcogenide glasses: GeSbTe and AgGeSe systems

M. FONTANA; M. A. UREÑA; B. ARCONDO; J. A. ROCCA; J. M. CONDE GARRIDO; M. ERAZÚ; A. PIARRISTEGUY

Oxford

Workshop; Oxford-Argentina Workshop; 2008

&amp;amp;lt;!-- /* Style Definitions */ p.MsoNormal, li.MsoNormal, div.MsoNormal {mso-style-parent:""; margin:0cm; margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:12.0pt; font-family:"Times New Roman"; mso-fareast-font-family:"Times New Roman"; mso-ansi-language:FR; mso-fareast-language:FR;} @page Section1 {size:612.0pt 792.0pt; margin:70.85pt 3.0cm 70.85pt 3.0cm; mso-header-margin:36.0pt; mso-footer-margin:36.0pt; mso-paper-source:0;} div.Section1 {page:Section1;} --&amp;amp;gt; One of the most important properties of some chalcogenide systems is their notable glass forming ability in broad composition ranges. Chalcogenide glasses have many technological applications as a result of their particular optic and electrical properties, e.g.: most of IV-VI basedglasses present an optical and electrical switching between two states: the glass and the crystalline state meanwhile several IV-VI glasses containing Ag or Li present, as a function of metal composition, a transition in electric transport from semiconductor to fast ionic conductor. The understanding of the glass structure, its transport properties, glass-crystal transition and its transformation kinetics is essential for these glasses application in non-volatiles memories as well as in solid state electrolytes. We present a survey of the fundamental properties of the two chalcogenide amorphous systems: GeSbTe and AgGeSe. Firstly, GeSbTe is very important system because of its application in CD, DVD technologies and non-volatile memories. We have obtained GeSbTe amorphous samples of compositions close to the eutectic point Ge15Te85 by rapid solidification of the liquid employing the melt-spinning technique. The glass forming ability of this system, for this cooling technique, is restricted to a small composition range nearby the binary eutectic. With the aim to application in non-volatile memories, the crystallization process of amorphous samples is analyzed employing differential scanning calorimetry and X-ray diffraction. The addition of Sb (in small quantities) to the eutectic point Ge15Te85 modifies the crystallization process. On the other hand, AgGeSe alloys can be applied as solid state electrolytes and were also recently studied and tested as new materials for building non-volatile memories. We have obtained AgGeSe amorphous samples by rapid solidification of the liquid employing the melt-quenching technique. The structure, thermal behavior and transport properties of these glasses are analyzed employing X-ray diffraction, differential scanning calorimetry, scanning electron microscopy, AC electric measurements and Mössbauer spectroscopy.  Agx(Ge0.25Se0.75)100-x is a fast ionic conductor with x>8 at% whereas it is a semiconductor for x<8 at%. One of the structural models proposed to explain the relation between transport and composition is based on an intrinsically inhomogeneous structure where, for lower x, zones rich in metals coexist with zones of the host material whereas for higher x this situation reverses. At the threshold concentration, a percolation transition is supposed. Scanning electron microscopy (SEM) and Mössbauer spectrometry are performed on amorphous Agx(Ge25Se75)100-x bulk samples corroborating the above mentioned hypothesis. Our research interests are: manufacture and characterization of chalcogenide glasses in bulk as well as in thin film. Study of the glass structure, composition determination, thermal behavior, phase transformation processes and transport properties.