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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 fo...

The new analysis of the previously published data on the nanocrystalline CaYTiNbO7:Eu indicates an occurrence of the size-induced structural phase transition like in other nanocrystalline phosphors of pyrochlore structure.

In the commented paper, there are some questionable data which should be explained or corrected by the Authors, Thangamani et al. In this comment, I have tried to pinpoint incorrect data or inconsistencies and to verify the correctness of the data presented in the crystallographic part of the paper.

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 ...

My comments concern the significant errors in the crystallographic part of the commented paper. It was found that the studied crystal is of the sillenite type and the correct formula should be Bi

My comments concern the severe errors in the crystallographic part of the commented paper. The correct formula is proposed to be Bi1-xGdxFeO3 instead of BiFe0.95Gd0.05O3. Thus, the actual composition of the studied crystal is not known. Furthermore, it is evident that the sample contains at least three different phases. The subsequent studies do not present the properties of the title compound.

The nanocrystalline LaMnO3+δ perovskite was synthesized by the microwave-assisted glycothermal method and calcined at several temperatures up to 1500°C. The prepared samples were examined by the X-...

My comments concern the significant error in the crystallographic part of the commented paper. It was discovered that the studied crystals are of sillenite type and the correct formula should be Bi25FeO39:Ni,Ti instead of BiFeO3. Moreover, the type of unit cell is not correct. Due to the doping the new type of unit cell, previously unknown, was proposed for such crystals. It was found that the studied sample contains two slightly different phases of the sillenite type. The actual chemical composition of the studied crystals is not known.

My comments concern the sever error in the crystallographic part of the commented paper. It was found that the studied crystal is of the sillenite type and the correct formula should be Bi25FeO39:Cd,Ti instead of some kind of solid solution based on BiFeO3. Moreover, the type of unit cell is not correct. Due to the double doping the new type of unit cell, previously unknown, was proposed for such crystals. The actual chemical composition of the studied crystals is not known.

Institute of Low Temperature and Structure Research of Polish Academy of Sciences celebrated its 50th anniversary in November 2016. The paper presents the history of the Institute going backward to the history of other ten scientific institutions from which the Institute was finally founded in 1966. It shows the efforts of Prof. Roman Ingarden and Prof. Włodzimierz Trzebiatowski to establish a powerful center of physics and physico-chemistry of solid state in Wrocław.

The crystal structure of the all studied compounds was refined in the monoclinic C2/m ( C 2 h 3 ) space group. The IR and Raman spectra of polycrystalline AgRE(WO4)2 have been recorded and analysed using the factor group approach. In the theoretical considerations the C2/m, P2/c and C2/c unit cell structures were taken into account. The change of the unit cell parameters induced by the RE ions exchange has been analysed. The assignment of the observed bands to the internal and external modes has been proposed. The verification of the structure has been done on the basis of the vibrational behaviour of the studied tungstates. Absorption, emission and excitation spectra of the investigated AgRE(WO4)2 polycrystals have been measured and analysed. The luminescence decay times of 5D0 → 7F2 (Eu3+) and 5D4 → 7F5 (Tb3+) transitions have been calculated.

The Pechini and microwave-assisted hydrothermal syntheses of nanocrystalline Er3+ and Tm3+ co-doped MY(WO4)2, where M = Li, Na, K, double tungstates are reported. The obtained samples were characterized using standard X-ray powder diffraction (XRD) technique, Rietveld method, transmission electron microscopy (TEM), scanning electron microscopy (SEM) and IR spectroscopy. The smallest crystallites (about 13 nm) could be obtained for the sodium samples synthesized by both the Pechini (for the resin calcined at 550 °C) and hydrothermal methods (synthesis at 230 °C). The average particle size of nanocrystalline powders increases with increasing temperature. It was found that nanocrystals retain the bulk structure with tetragonal and monoclinic symmetry for the sodium and potassium analogues, respectively. In contrast to this behaviour, LiY(WO4)2 undergoes a size-induced structural transformation from monoclinic (space group P2/n) to tetragonal (space group I41/a) symmetry. IR spectra of the synthesized sodium and potassium compounds are very similar to their bulk counterparts. IR spectra of the lithium analogues show, however, abrupt changes when the calcination temperature increases to 850 °C or higher. This behaviour is consistent with the size-induced phase transition in this compound.

The commented paper contains many errors in the crystallographic analysis of the diffraction data received by the Authors. The main error is that the data do not correspond to the title crystal.

The commented paper presents the results on structural and optical studies on the nanocrystals of SrAl2O4:Eu. Unfortunately, there are mistakes in the analysis of diffraction patterns in this paper which should be corrected to avoid its use in the future papers by Authors and by other people.

A non-centrosymmetric, polar La 2 CaB 10 O 19 single crystal was characterized by polarized Raman scattering and polarized infrared reflection spectroscopy at room temperature. Assignment of the observed modes to the respective vibrations of its structural units has been proposed. Based on these results, the LO–TO splitting has been determined for the observed modes. Thus, large LO–TO splitting was observed for B O stretching modes, whereas the lower wavenumber modes assigned to bending and lattice modes exhibited small splitting. Our results also show that the LCB crystal is promising SRS-active material for use as a Raman laser frequency converter.

Na 3 RE(PO 4 ) 2 orthophosphates, where RE = Y and Gd, doped with Yb 3+ ions were synthesised by hydrothermal method and characterised by X-ray diffraction, microscopic, IR and Raman techniques. The emission, excitation spectra were recorded at room temperature and fluorescence decay time was determined. As-synthesised samples crystallise in a trigonal modification and during calcination at 500 °C they transform to a monoclinic or orthorhombic symmetry (for yttrium and gadolinium compounds, respectively). Finally, the samples calcined at 700 °C do not reveal the trigonal symmetry. The morphology of particles for all samples is similar and resembles rice grains. All the obtained for the studied orthophosphates data were compared to those previously reported for the same compounds synthesised by Pechini method.

The correct values of crystallites size of Y2SiO5 powder are presented as a correction of data published in the commented paper. Additionally, the description of the size-induced phase transition is given.

Fourier transform IR and Raman spectra of the Cd1−3xGd2x□xMoO4 solid solutions have been studied and analysed using the factor group approach (□ denotes the cationic vacancies). The tetragonal I41/a (C4h6) space group with Z = 2 have been applied in the discussion. The assignment of the bands observed to the internal and external modes has been proposed and related to the formation of the solid solutions in which the gadolinium content has been changed in the range 0–1.0. The optical spectroscopic studies show visible dependence of the transition corresponds to the cationic vacancy on the Gd3+ content. The correlation between the crystallographic and spectroscopic data has been discussed in terms of the structural changes of the solid solutions induced by the defects in the CdMoO4 host lattice.

Cadmium-rare earth Cd 0.25 RE 0.5 □ 0.25 MoO 4 molybdates, where RE = Pr–Dy, have been prepared and characterised by powder XRD analysis and spectroscopic studies. IR and Raman spectra at room temperature have been measured in the MIR and FIR ranges. The correlation between the lattice parameters and spectroscopic data has been discussed in terms of factor group analysis. The dependences between the RE 3+ ionic radius, atomic mass and IR and Raman wavenumbers have been discussed.

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 defini...

The rod- and stick-shaped nanocrystalline cerium and lanthanum orthophosphates, pure and Pr 3+ doped, have been synthesised by the hydrothermal method in acidic (pH 1) or alkaline (pH 11) environment. Subsequent calcination of as-obtained powders at different temperatures, 500 and 900 °C, led to the formation of hexagonal and monoclinic phases, respectively. The hexagonal phase at room temperature has been identified as hydrated orthophosphate with zeolite water inside the channels of the structure. The monoclinic phase is free of water. The average grain size is about 12–30 nm depending on the calcination temperature and preparation conditions. The structural, morphological and optical (vibrational and luminescent) properties have been characterised and their changes due to the temperature and different acidity in the starting materials have been studied.

Nanosized Bi2WO6 was synthesized by a mild hydrothermal crystallization process. This method allowed obtaining plate-like crystallites of very small thickness (down to 3 nm). The effect of particle size on the structure and properties of Bi2WO6 was studied by X-ray diffraction (XRD), transmission electron microscopy, and Raman and infrared spectroscopies. It has been shown that the orthorhombic distortion decreases with decreasing particle size, but the structure of the smallest crystallites is still orthorhombic. Raman studies have also revealed a very strong intensity decrease for those modes that appear mainly for incident and scattered light polarized perpendicular to the layers. This behavior has been attributed to a decrease in the orthorhombic distortion and a plate-like shape of the nanocrystallites. Copyright © 2009 John Wiley & Sons, Ltd.

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.

The luminescent nanocrystalline KEu(WO4)2 and KGd0.98Eu0.02(WO4)2 have been prepared by the Pechini method. X-ray diffraction, infrared and Raman spectroscopy as well as optical spectroscopy were used to characterise the obtained materials. The crystal structure of KEu(WO4)2 was refined in I2/c space group indicating the isostructurality to KGd(WO4)2. The size of the crystalline grains depended on the annealing temperature, increasing with the increase of the temperature. The average size of crystallites of both crystals formed at 540 °C was about 50 nm. Vibrational spectra showed noticeable changes as a function of size due to, among others, phonon confinement effect. Luminescence studies did not reveal significant changes for the nanocrystallites with the lowest grain size in comparison with the bulk material. The differences observed in luminescence spectra in form of slight inhomogeneous broadening of the spectral lines and increase of the hypersensitive I0–2/I0–1 ratio point to very low symmetry of Eu3+ ions and change of the polarisation of the local vicinities of Eu3+. X-ray diffraction, vibrational and optical studies showed that the structure of the synthesised nanocrystalline KEu(WO4)2 and KGd(WO4)2:Eu is nearly the same as that found for the bulk material. The size-driven phase transitions were established for both compounds.