Nanocomposites and nanomaterials

Crystallization of the amorphous phase and 
electrical properties of lithium-sodium tetragermanate 
Diachenko A.O., Trubitsyn M.P., Volnianskii M.D., Skrypnik Y.V.
 
1 Department of experimental physics, Oles Honchar Dnipro National University, prosp. Gagarina 72, Dnipro-49010, Ukraine.

E-mail: annadiachenko459@gmail.com

In recent years, lithium ionic conductivity has been actively studied in the compounds of lithium germanium oxides family.  Lithium-sodium tetragermanate Li2-xNaxGe4O9 (x=1) (LNG) is one of the representatives of this family which was the object of numerous experimental studies.  Earlier it was shown that conductivity σ of these crystals was determined by Li interstitials moving along the channels of the crystal structure [1].  It is known that ionic conductivity is strongly dependent on the structure on nano- and micrometer levels.  Usually σ is significantly higher in amorphous phase in comparison with crystalline one.  Taking into account the data on conductivity of LNG single crystals [1], it is of interest to study the charge transfer in the glass of the same chemical composition.
In this work we study crystallization of LNG glass and changes of σ during devitrification process.  LNG glass was prepared by fast quenching the melt.  Technological conditions and regimes were the same as given in [2].  Crystallization processes on heating LNG glasses were studied using differential thermal analysis (DTA) and measuring temperature dependences of electrical conductivity.  DTA was carried out in the temperature range of 290–1200 K at a heating rate of about 20 K/min.  Measurements of σ (T) were performed by bridge method in AC field in the temperature range 300–950 K.
DTA demonstrated the exothermal peak manifested devitrification of LNG glass.  On heating σ(T) behavior reflected glass crystallization and sharply changed around DTA peak.  It was shown that LNG glass can be crystallized by two ways: by heating and by isothermal treating near below the devitrification temperature.  Thermal treatment made it possible to turn LNG glass into intermediate nanocrystalline states similar to studied earlier in lithium heptagermanate [2]. Changes of conductivity in the LNG intermediate state was connected with mobile Li ions moving within nanocrystalline nuclei imbedded into glass matrix.  It was shown that preparation of LNG glass-ceramics allowed to control ionic conductivity in a wide range. 

1.	 Volnianskii M.D., Trubitsyn M.P., Bibikova O.A.  Electric Properties of LiNaGe4O9 Single Crystal // Ferroelectrics.- 2013.- V.443.- P.16-19. 
2.	 Volnianskii M.D., Nesterov O.O, Trubitsyn M.P.  Devitrification of the Li2O – x(GeO2) Glass // Ferroelectrics. - 2014. - V.466. - P.126-130.