«New Materials – New Properties» Partner Group

Partner Group «New Materials – New Properties» of
Max Planck Institute for Chemical Physics of Solids and
Chemistry Department of Moscow State University

Anastasia M. Alekseeva*, Oleg A. Drozhzhin*, Sergey Ya. Istomin*, Varvara V. Chernova*, Kirill A. Dosaev*, Cevriye Koz, Helge Rosner, Zhiwei Hu, Liu H. Tjeng and Yuri Grin

A Partner Group «New materials – New properties» of MPI CPfS and Chemistry Department of Moscow State University was established in 2011. The foundation of the Partner Group was a result of the intensive scientific collaboration between Chemistry Department of the MSU and MPI CPfS. Since 2002 the fruitful joint studies have been performed in different fields of inorganic chemistry, solid state chemistry and solid state physics. During this time more than thirty joint papers were published and four Ph.D. theses were defended. The aim of the Partner Group was primary defined as the prolongation and expansion of the scientific collaboration targeted to the actual research tasks on the mutually interesting fields.

The Partner Group activities involve the specialists from different fields of material research: chemistry of non-oxide compounds; structure and properties of the perovskite related phases; solid state electrochemistry and Li-ion batteries.

The essential activity of the Partner Group was targeted to the building of the experimental setup. Mainly, it concerned the development of the experimental facilities for electrochemical preparation and investigation: upgrading the glove box system for electrochemical studies of air- and moisture-sensitive materials; development of the electrochemical cell design, including specific cell design for high/low temperature experiments and experiments with non-commercial electrolyte; development of the setup for in-situ X-ray diffraction experiment.

Research activity of the Partner Group is divided by two main directions:

Electrochemical preparation of new nonoxide materials

The interest to the investigation of the electrochemical intercalation of metal cations into non-oxide compounds is related either to the fundamental or applied aspects. The fundamental aspect is the development of a new synthetic approach using electrochemical potential as a «driving force» of chemical reaction (similar to temperature and composition in routine solid state synthesis). It can promote a low-temperature synthesis of new «metastable» compounds unreachable by routine solid state synthesis. One of the most impressive examples of such electrochemically synthesized compounds is lithium cobalt oxide Li1–xCoO2. Application of Li1–xCoO2 as cathode in Li-ion batteries allowed to start ones large-scale production. Compared to
chemical modification, electrochemical intercalation can possess extra advantages, namely the possibility to control the intercalation process by varying the potential, composition of
electrolyte, reaction time and temperature. The applied aspect of the non-oxide intercalation matrixes investigation relates to the development of the multivalent ion batteries, namely, magnesium batteries. The only functional prototype of Mg-batteries, existing today, was designed using non-oxide cathode MgxMo6X8 (Chevrel phase), where 0 < x < 2 and X = S, Se. It should be noted that numerous attempts to use solid state oxides (used Li+-intercalation matrixes) for Mg2+-intercalation were unsuccessful. This required to change the concept of the cathode material search for Mg-batteries as compared to Li-ion batteries and to focus on the non-oxide compounds. The additional fundamental aspect is a rather poor (compared to oxides) amount of data concerning electrochemical behavior of non-oxide compound upon metal cation intercalation. The research in this direction was primary aimed at studying the electrochemical Li intercalation into non-oxide structures targeted to structure and properties modification.

Investigation of the spin state of Co3+ in A2(Co,Ga)2O5, A = Ca, Sr cobaltates with the brownmillerite structure

Spin states of Co3+ (low spin (LS, S = 0), high spin (HS, S = 2) and intermediate spin (IS, S = 1)) and relevant transformations between them are among basic microscopic features of Co-based oxide materials. Co3+-contained perovskites possess both electronic and oxide-ion conductivity at high temperatures, that supposes them to be promising materials for high-temperature electrochemical devices like cathodes for intermediate temperature solid oxide fuel cells or dense ceramic membranes to separate oxygen from gas mixtures. One of the
main drawbacks of cobaltates is their high thermal expansion coefficient (TEC) exceeding 20 ppm K-1 for LaCoO3. High TECs for cobalt-related perovskites are due to the temperature activated LS-HS transitions of Co3+. The aim of the presented research consists in understanding how to influence on spin state of Co3+ in perovskiterelated cobaltates by variation of their cation composition in order to design materials operating in a wide temperature range. As research objects A2(Co,Ga)2O5, A = Ca, Sr compounds with brownmillerite structure have been chosen.
The results of the Partner group research in 2011–2014 have been published in 3 articles and presented at 4 international conferences. Currently one more manuscript is prepared for publication. Four workshops held alternately in Moscow and in Dresden were organized.

* MPG-MSU Partner Group, Department of Chemistry, Lomonosov Moscow State University, 119991 Moscow, Russia

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