Size-induced phase transitions

ABSTRACT

This paper presents a holistic view of the structural phase transitions in nanocrystals. The databases for size-induced phase transitions is a main part of this paper. The database on transitions with temperature contains 603 items on 415 crystals, and database on transitions under high pressure contains 209 items in 124 crystals. Moreover, some new aspects of such transitions are presented like island diagram and new analysis of anomalous compressibility observed in some nanocrystals.

KEYWORDS:

• Phase transitions
• nanocrystals
• databases
• high pressure
• crystallite size
• island diagram

Disclosure statement

No potential conflict of interest was reported by the author(s).

Notes

1 In general, there are various processes during grinding:

• induction of phase transition

• induction of a chemical reaction (we do not consider this!)

• change of particle and crystallites size

• a large number of defects are formed

• controversies about raising the sample temperature and/or pressure

2 Their ‘nanocrystal’ has a diameter of 0.7 nm, i.e. 7 Å, while the unit cell has lattice parameter of about 5.5 Å!

3 The term ‘high temperature phase’ refers to a phase occurring at high temperatures and accessible only by heating the sample in a (quasi)continuous process. On the other hand, if the sample is heated for a long time at a certain temperature, the term ‘high-size phase’ should be used for the crystal phase so obtained, as this phase has larger crystallites than before annealing.

4 I omit situations in which we observe linear negative compressibility, i.e. an anomalous increase of one of the unit cell parameters while maintaining decreasing volume of the unit cell (e.g. for La₁₀Si₆O₂₇: [35]).