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My comments concern the significant errors in the crystallographic part of the commented paper. The diffraction patterns are erroneously analysed and the final chemical composition is different than those supposed in the paper. There are also some manipulations with data. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The new form of the phase diagram is proposed for nanocrystals. This island diagram shows the regions of the calcination temperature required to obtain the nanocrystals of given range of crystallite size. This explains why the temperature-induced phase transitions are not possible in some crystals. However, the change of crystallite size can induce the phase transition. [ABSTRACT FROM AUTHOR]

My comments concern the severe errors in the crystallographic part of the commented paper. The correct formula is proposed to be Bi1–xYxFeO3 ('Bi0.85Y0.15FeO3') instead of BiFe0.85Y0.15O3. It is found that the studied sample is bi-phasic with nearly equal amounts of BiFeO3:Y and Bi25FeO39:Y. The actual composition of the studied crystals is not known. Moreover, the type of unit cell is not correct. [ABSTRACT FROM AUTHOR]

I would like to comment the crystallographic part of the paper by Santosh Kumor Parida and Rama Narayan Prasad Choudhary entitled 'Preparation method and cerium dopant effects on the properties of BaMnO3 single perovskite' and published in 'Phase Transitions' in September 2020 [1]. There are several errors that should be corrected, if possible. [ABSTRACT FROM AUTHOR]

My comments concern the significant errors in the crystallographic part of the commented paper. [ABSTRACT FROM AUTHOR]

The literature data on the smallest unit cells as well as on the smallest single crystals studied by X-ray diffraction are reviewed. Different types of phase diagrams “temperature—grain size” are presented and discussed. The literature data on the grain-size driven structural phase transitions occurring in nanocrystals (quantum dots) are presented in the form of a database. It was found that there were no reports on phase transitions occurring for nanocrystalline grains with a linear dimension smaller than 7 unit cells. The grain-size driven phase transitions for some nanocrystalline double tungstates, molybdates and phosphates are also described. [ABSTRACT FROM AUTHOR]

The correct values of crystallites size of Y 2 SiO 5 powder are presented as a correction of data published in the commented paper. Additionally, the description of the size-induced phase transition is given. • The size-induced phase transtion is discovered. • The correct values of crystallite sizes have been presented. • The correction of errors in the previously published paper is presented. [ABSTRACT FROM AUTHOR]