Heat Capacity of Decagonal and Icosahedral Quasicrystalline Phases at High Temperatures

O O Levkovich,Yu V Syrovatko

doi:10.15330/pcss.21.2.260-265

Abstract

The paper deals with the calculations of heat capacity of quasicrystalline decagonal Al69Co21Ni10 and icosahedral Al63Cu25Fe12 quasicrystalline phases of Al–Co–Ni and Al–Cu–Fe alloys, respectively. According to the Gruneisen law, heat capacity is an energy characteristic, which reflects the phases’ resistance to failure. For calculations of the heat capacity, structure of quasicrystalline phases is considered in the model representation of anisotropic crystals. As a result, it is found that the heat capacity of quasicrystalline phases at high temperatures is the excessive one, i.e. it exceeds the Dulong-Petit value. Therefore, quasicrystalline phases at high temperatures are more stable, than the crystalline phase. For the decagonal quasicrystalline phase, heat capacity is more than 3R in the temperature range of ~480–1500 К, and for the icosahedral quasicrystalline phase – in the temperature range of ~380–1120 К. It follows that decagonal phases remain stable at high temperatures at which the icosahedral phases are destroyed.

Highlights

The unique structure of quasicrystals determines their unusual physical and chemical properties
In the course of manufacturing of the composite materials with quasicrystalline fillers, the question arises with regard to stability of quasicrystalline phases to the temperature action of the molten binder
The quasicrystalline decagonal phases are destroyed at higher temperatures [3, 4] than the icosahedral phases

Summary

Introduction

The unique structure of quasicrystals determines their unusual physical and chemical properties. Quasicrystals have low coefficients of friction and surface tension, as well as high hardness, durability and corrosion resistance. Owing to these properties, quasicrystals find their practical use in the form of films, coatings and components of the composite materials. In the systems of Al–Cu–Fe and Al–Ni–Co the icosahedral Al63Cu25Fe12 and decagonal Al69Co21Ni10 quasicrystalline phases, respectively [1, 2], are found. In order to explain the phenomenon of the excessive heat capacity of quasicrystalline phases, as well as the fact of stability of decagonal phases at higher temperatures, this paper deals with the heat capacity of phases from the standpoint of the model of anisotropic crystals [8]

Model representation of the structure of crystalline phase

Model representation of the structure of quasicrystalline icosahedral phase

L 1 4 12

Analysis of results

Conclusions