Paweł E. Tomaszewski

Structural phase transitions in crystals. I. Database

Abstract The database on structural phase transitions is presented in the simple and easy accessible form of table. The symmetry changes and temperature for 3446 phase transitions and the references for each of 2242 registered crystalline materials with well defined stoichoimetry are the main data in this table. The rules for constructing and reading the database table are also presented.

X-ray study of the low-temperature phase transitions in LiKSO4

Abstract Lattice parameters of LiKSO4 have been measured in the temperature range 155–300 K with an X-ray single-crystal Bond diffractometer. Below 180 K LiKSO4 transforms on cooling into an orthorhombic phase. Above this temperature there is a broad range of an intermediate hexagonal phase which depends on the real structure of the sample and differs considerably on cooling and on heating. The anomalies in the physical properties of LiKSO4 reported in the literature have been explained. The crystal structure of the low-temperature and intermediate phase, as well as the mechanism of the phase transitions, are suggested and discussed.

X-ray and optical study of the phase transition in LiCsSO4

Abstract Lattice parameters of LiCsSO4 have been measured in the temperature range 160–550 K with an X-ray single-crystal Bond diffractometer. The monoclinic angle γ in the low-temperature ferroelastic phase has been interpreted as an order parameter. Detailed results of X-ray studies of the ferroelastic domain structure supported by observations under a polarizing microscope are presented. An earlier report on the existence of an intermediate phase in LiCsSO4 has not been confirmed.

Dielectric measurements and domain structure in LiKSO4 at low temperatures

Dielectric measurements in the temperature range 33-300K with simultaneous optical observations on LiKSO4 slabs perpendicular to the c hexagonal axis have been performed. A few dielectric anomalies and domain textures are obtained according to the different thermal treatments. A specific thermal treatment has been found allowing reproducible results. Previous contradictory results in the literature can therefore be explained.

Phase transitions in LiKSO4 at low temperature

Abstract First optical observations of the domain textures and simultaneous dielectric measurements in LiKSO4 at low temperature are presented. Reproducible results were obtained under specific thermal treatment.

The uncertainty in the grain size calculation from X-ray diffraction data

The phase transition, usually called size-induced phase transition (SIPT), occurs at a threshold crystal diameter – critical grain size. The first published database and classification of such phase transitions [P.E. Tomaszewski, Phase transitions in extremely small crystals, Ferroelectrics 375 (2008), pp. 74–91] listed the set of critical values for known SIPT. Now it becomes clear that the published values have a limited scientific significance due to several factors influencing the calculated values of the critical diameter and grain size. Thus, a simple question arises – is the accurate grain size evaluation possible? The answer is NO. Unfortunately, none of the known methods give the correct value for the crystallite size of nanocrystals! It is only possible to talk about the range of values. Finally, it should be emphasized that all published values for the threshold crystal size of SIPT are not correct! The way to partially solve this serious problem is to provide the detailed description of definitions, methods, etc.

Lattice dynamics and phase transitions in KAl(MoO4)2, RbAl(MoO4)2 and CsAl(MoO4)2 layered crystals

Raman and IR studies of KAl(MoO4)2, RbAl(MoO4)2 and CsAl(MoO4)2 are reported. The assignments of modes are given on the basis of lattice dynamics calculations. The temperature dependence of the KAl(MoO4)2 vibrational modes shows that this compound exhibits a second-order phase transition around 90 K from the to most probably a monoclinic and ferroelastic phase.

Jan Czochralski—father of the Czochralski method

Abstract A critical review of papers concerning the invention of the “Czochralski method” is presented. It is beyond all doubt that this method of pulling single crystals from the melt should be named after the Polish scientist, chemist and metallurgist J. Czochralski. The recent curious supposition by H.J. Scheel to change the name of this method should be ruled out as being without scientific value and in contradiction to historical data.

CsAl(MoO4)2

The title compound, caesium aluminium dimolybdate(VI), CsAl(MoO4)2, belongs to the glaserite type family of double molybdates and tungstates. The crystal structure was studied by in situ X-ray single-crystal and powder diffraction at room temperature. The temperature dependence of the lattice parameters at low temperatures is also presented.

Phase Transitions in Extremely Small Crystals

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.