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Super-Ionic Chalcogenide Glasses

#A-1403


Super-Ionic Conductors on the Basis of Multi-Component Chalcogenide Glasses

Tech Area / Field

  • MAT-SYN/Materials Synthesis and Processing/Materials

Status
3 Approved without Funding

Registration date
20.03.2006

Leading Institute
Institute of Electronic Materials, Armenia, Yerevan

Collaborators

  • University of California / Department of Physics, USA, CA, Davis\nUniversity of Chicago, USA, IL, Chicago\nUniversity of Cambridge / Department of Chemistry, UK, Cambridge\nSlovak University of Technology / Faculty of Materials Science and Technology, Slovakia, Trnava\nCNRS / Université de Rennes 1, France, Rennes\nUniversity of Pardubice, Czechia, Pardubice\nUniversität Rostock / Department of Physics, Germany, Rostock\nUniversity of Montreal / Départment de Physique, Canada, QC, Montreal

Project summary

In the framework of the current Project it is proposed to investigate glass-formation and glasses properties in multi-component As-Ge-Se-S-Te-Ag-J system in order to develop new super-ionic materials, which are perspective in terms of their application as solid electrolytes in structures of rechargeable micro-batteries, sensors, indicators, etc.

The existing glasses with super-ionic conductivity are vitreous solid materials, which ionic conductivity at room temperature is σ~10-2 (Om-1·cm-1). This value is much higher than the values for gel-like and liquid polymers (10-4 Om-1·cm-1). However, the need for higher conductivity values along with higher chemical and thermal stability stimulates to continue searching new optimized materials applicable in severe environmental conditions. Thus, the urgency of elaboration of such materials is obvious.

The selected system will provide an opportunity to develop new vitreous materials with ionic conductivity exceeding the conductivity of existing materials. In addition, it will allow more about the ionic conductivity mechanism in chalcogenide glasses to learn.

The goal of this Project is:

  1. Conduct a research on glass formation and glasses properties in multi-component As-Ge-Se-S-Te-Ag-J system.
  2. Determine the correlation between composition, properties, local structure and ion transfer process for glasses of the above-mentioned system.
  3. Optimize the compositions of glasses in terms of maximal ionic conductivity, satisfactory electrochemical stability that are prospective as new solid electrolytes.

It is known that the optimization of ionic conductivity in glasses mainly caused by the choice of the charge carrier and by increasing its mobility that is directly connected to the structure of received glasses.

According to literature, the ions of silver maximize ionic conductivity of glasses due to their high polarizability. The choice of chalcogenide system as glass-matrix in its turn ensures increased mobility of silver cations. This is explained by weaker coulomb bonding of silver ions with structural lattice of chalcogenide glasses compared to oxide glasses.

Currently, the highest values of ionic conductivity were obtained in selenide system glasses. Three chalcogens (S, Se, Te) combination in system promotes structural units formation in glass matrix containing different chalcogens atoms that will lead to higher lattice polarizability compared to inpidual sulfide or selenide lattices, which, in its turn, will increase the mobility of silver ions.

Multi-component system on the basis of three chalcogens will result in the extension of glass-forming range that will make possible to introduce the silver into glass structure (up to 40 at %) to the maximum. We proved this in our laboratory earlier during the process of photosensitive chalcogenide glasses elaboration for optical recording system on the basis of As-Se-S-Te-Sb multi-component system.

We suppose that so called effect of mixed glass-forming elements will be observed in a selected multi-component system. This effect is connected to nonlinear growth of conductivity at mixing of various glass forming elements.

The mechanism of ionic conductivity in glasses is not as trivial. Despite the extensive research conducted during the last decades, there is no theory explaining the process of ionic conductivity on a micro-level.

Development of new materials is still based on experiment and common practice rather than on fundamental understanding of the nature of conductivity.

Nevertheless, the latest investigations have shown that glasses with different molecular structure are characterized by different mechanisms of charge transport. This phenomenon is well illustrated on the example of (GexSe1-x)1-yAgy three-component system, where the silver can be both a glass-modifier and a glass-builder depending on proportion of selenium and germanium.

In the first case, the silver modifies the structure of matrix glass and creates the new phase enriched with Ag2Se, which is actually an electrolyte component providing ionic conductivity. The fact of availability of two-phase structure is reflected in the form of bimodal distribution of glass-transition temperatures (i.e. two values of Tg).

In the second case, the introduction of silver leads to germanium substitution in glass lattice with formation of the structural units that are triple-coordinated by selenium (AgSe3/2). These units are built in the common germano-selenium network. Here, the silver functions as a structure builder, by common germanium-silver-selenium lattice formation. In this case the silver loses its mobility as cation and creates the acceptor levels near the valence band as an admixture by becoming the source of electronic (p-type) conductivity initiation. Thus, for obtaining vitreous materials with super-ionic conductivity it is necessary to provide the conditions for maximal delocalization of silver ions in glass structure, namely, the added silver must mainly play a role of glass modifier. These conditions can be realized relatively easy in a multi-component system.

Results obtained in our laboratory in the process of chalcogenide glass development for recording and sealing layers have shown a beneficial effect of iodine atoms on homogenous glasses obtaining that mainly is conditioned by -AsJ- and GeJ2- grouping appearance with two bonds, which formally may be considered as pseudo-chalcogens.

In addition to decreasing the crystallization ability, the introduction of iodine into multi-component system will result in the certain loosening of structure lattice and increasing silver ions mobility.

In the process of the proposed Project implementation the following tasks will be completed:

  1. Elaboration of ionic conductivity measurement methods for chalcogenide glasses in wide temperature range.
  2. Identification of the silver role both as a modifier and as a builder in various concentration range of Ge-As-S-Se-Te-J-Ag system by means of measuring conductivity and conducting dilatometric investigation.
  3. Investigation of iodine influence on silver ions mobility in multi-component systems As-Se-S-Te-Ag-J.
  4. Interpretation of ionic transport mechanism depending on structure of argentiferous multi-component glasses.
  5. Investigation of synthesis of optimized glasses having maximal ionic conductivity, which is prospective in terms its application as solid electrolyte.

The scientists from the Scientific-Production Enterprise of Material Science – SPEMS has great experience in the field of chalcogenide glasses development of various purposes. There are all reasons to believe that combined experience and efforts of the team will allow the problems stated in the proposed Project successfully and timely to solve.

Authors of the Project invite the scientists, research organizations, as well as private experts and scientists from the USA, Canada, the countries of the European community, Japan, Korea for collaboration.

In addition, we propose to conduct joint seminars and scientific research on the discussed problem.


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