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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...

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 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-...

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.

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...

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.

NaIn(WO 4 ) 2 :Cr 3+ nanoparticles have been prepared by Pechini method. Resultant samples have been characterized by X-ray, transmission electron microscopy, Raman, infrared, absorption and luminescence. The average particle size of NaIn(WO 4 ) 2 :Cr 3+ formed at 460 °C was about 46 nm and increased with the increase of annealing temperature. Vibrational spectra showed significant changes as a function of size which were explained as a result of phonon confinement effect. Luminescence studies revealed that the inter-electronic repulsion in the shell of d orbitals as well as covalent character of the chromium environment remains nearly the same irrespective of the nanocrystallite size. However, the strength of the electron–phonon coupling decreases with decreasing size of nanoparticles.

Single crystals of potassium magnesium phosphate KMg 4 (PO 4 ) 3 have been obtained from flux and characterized by means of single-crystal X-ray diffraction method and IR and Raman spectroscopy. This compound crystallizes in the Pnnm space group with a = 16.361 ( 3 ) , b = 9.562 ( 19 ) , c = 6.171 ( 12 ) A and Z = 4 . The structure is built up of PO 4 tetrahedra, MgO 6 octahedra and MgO 5 polyhedra connected via P O Mg bridges to form a three-dimensional framework enclosing tunnels along b -axis occupied by K + ions. IR and Raman spectra are consistent with the crystal structure. The internal and external modes are observed in the 350–1210 cm −1 range and below 330 cm −1 , respectively.

The crystal structure of the paraelastic phase of KFe(MoO4)2 at 360 K was reinvestigated and high pressure Raman scattering experiments were performed on this material. The studies indicated that this molybdate crystallizes in the structure above 312 K. At room temperature the structure is monoclinic and it transforms under pressure into , and low symmetry phases at 0.25, 1.3 and 1.6 GPa, respectively. The phase transitions observed at 0.25 and 1.6 GPa are irreversible whereas the 1.3 GPa transition is reversible. The lattice dynamics calculations performed for the phase allowed us to obtain an assignment of observed modes and helped us to obtain insight into the mechanism driving the structural changes occurring in this material. The x-ray study of the highest pressure phase, recovered during the decompression experiment, shows that the crystal structure of this phase is monoclinic or triclinic. When this phase is subjected to heat treatment at 673 K, it either transforms into another phase or decomposes.

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.

Heat capacity and dielectric properties of RbNbWO 6 were measured as a function of temperature. The heat capacity measurements revealed the presence of two discontinuous phase transitions at 356.5 and 361.6 K. The former transition was attributed to a transition from the low-temperature tetragonal ferroelectric phase to a phase of unknown symmetry, and the latter to a transition to the cubic phase. The dielectric study revealed the presence of only one and broad anomaly below 310 K. The real and imaginary parts of dielectric permittivity show pronounced shifts of the maxima towards higher temperature with increasing frequency. This behaviour has been attributed to a relaxation process and it seems to be not correlated with the paraelectric–ferroelectric phase transition.

Some statistical analyses of data from the database are presented in the form of special diagrams. These indicate the frequency of occurrence of phase transitions with the given change of crystal system. These diagrams have been prepared for all phase transitions for which the symmetry of both phases is known (2480 entries) as well as for ferroelectric crystals and incommensurate phase transitions.

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.

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.

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.

Lattice parameters of NH4BeF3 have been measured in the temperature range 235–365 K with an X-ray single-crystal Bond diffract meter. DSC measurements and Weissenberg photographs are also described in both the high-and low-temperature regions, and the phase diagram is presented. On heating, NH4BeF3 transforms at 334 K to an intermediate phase and at 347 K to the high-temperature phase.