Space Group P4bm Research Articles

Crystal structure of propane-1,3-diaminium squarate dihydrate.

Propane-1,3-diaminium squarate dihydrate, C3H12N2 2+·C4O4 2-·2H2O, results from the proton-transfer reaction of propane-1,3-di-amine with squaric acid and subsequent crystallization from aqueous medium. The title compound crystallizes in the tetra-gonal crystal system (space group P4bm) with Z = 2. The squarate dianion belongs to the point group D 4h and contains a crystallographic fourfold axis. The propane-1,3-diaminium dication exhibits a C 2v -symmetric all-anti conformation and resides on a special position with mm2 site symmetry. The orientation of the propane-1,3-diaminium ions makes the crystal structure polar in the c-axis direction. The solid-state supra-molecular structure features a triperiodic network of strong hydrogen bonds of the N-H⋯O and O-H⋯O types.

The crystal structures of the ternary intermetallics RE 2Pd2Cd (RE = Nd, Sm, Gd, Dy) and RE 2Ga2Mg (RE = Tb, Er, Tm, Lu) at 90 K

Abstract The crystal structures of the U3Si2-related intermetallic compounds RE 2Pd2Cd (RE = Nd, Sm, Gd, Dy) and RE 2Ga2Mg (RE = Tb, Er, Tm, Lu) were studied from single crystal X-ray diffraction data at T = 90 K in order to understand the slightly enhanced U 33 displacements of the 2a positions in their room temperature structures. The compounds Sm2Pd2Cd, Gd2Pd2Cd and Dy2Pd2Cd show a decrease of the ratio of U 33 to U 11 for the cadmium atoms, leading to a more isotropic behavior at low temperature, keeping the P4/mbm space group symmetry. Nd2Pd2Cd shows a translationengleiche symmetry reduction to space group P4bm along with a weak puckering effect with shorter (342.7 pm) and longer (345.7 pm) Cd–Nd distances within the Cd@Nd8 square prisms. This new, non-centrosymmetric superstructure variant was also observed for the magnesium compounds Tb2Ga2.069Mg0.931, Er2Ga2.104Mg0.896, Tm2Ga2.097Mg0.903 and Lu2Ga2.173Mg0.827, which show small degrees of Mg/Ga mixing.

Unveiling the role of ZrO2 doping in Sr2SmTi2Nb3O15 ceramics: From structural study to dielectric enhancement

Solid-state processing was used to synthesize tungsten bronze type (TTB) solid solutions, specifically Sr2Sm(Ti1-xZrx)2Nb3O15 with x values of 0, 0.2, 0.3, and 0.4. The study examined the crystalline structure, optical properties, morphology, and electrical and dielectric characteristics of these compounds. X-ray diffraction revealed a tetragonal structure (space group P4bm). Scanning electron microscopy showed significant sample densification with grain sizes decreasing from 6.19 μm to 2.78 μm. Dielectric measurements indicated that the dielectric constant varied from 150 for x = 0 to 567.24 for x = 0.2, then decreased to 380.88 for x = 0.4, with the x = 0.3 compound having the lowest dielectric loss. The Curie temperature (Tc) decreased from 332 °C to 248.5 °C with increasing Zr content, corresponding with a reduction in grain size. The energy gap (Eg) narrowed from 2.914 eV to 2.714 eV as Zr content increased. AC conductivity increased with temperature and frequency. Electrical conductivity followed Jonscher's power law, with activation energies decreasing from 1.54 eV to 0.87 eV, explained by the small polaron tunneling (NSPT) model.

Ferrimagnetic transition, relaxor ferroelectric and optical properties in tungsten bronze Ba6MnNb9O30 ceramics

The structural, magnetic, ferroelectric, dielectric and optical properties of Ba6MnNb9O30 (BMNO) and Ba6Mn0.5Co0.5Nb9O30 (BMCNO) ceramics were investigated. The samples can be indexed by a tetragonal lattice and the space group of P4bm with the presence of a tiny amount of impurity phase Ba1.04NbO3. The sample BMNO undergoes a short-range ferrimagnetic-like transition at 43 K originating from the spin canting of the antiferromagnetic coupling between the adjacent Mn2+ and Mn3+ based sublattices via the Dzyaloshinskii-Moriya interaction, whereas the sample BMCNO exhibits a local short-range antiferromagnetic state with the presence of weak ferromagnetic ordering. Both samples show the relaxor ferroelectric nature. The sample BMCNO possesses a superior energy storage property with a total energy density of 1.58 J/cm3 and a conversion efficiency of 74.5 %, which can be mainly ascribed to the improved densification and the reduced oxygen vacancies. Two different dielectric relaxations are discussed in term of the Vogel-Fulcher law. In addition, all samples have two different absorption edges and the optical band gaps are determined to be about 2.2 eV and 2.8 eV.

The effects of Sr-substitution in Ba2SmTi2Nb3O15 ceramics: structural study, optical properties, and complex impedance spectroscopy.

Ceramics of (Ba1-xSrx)2SmTi2Nb3O15, denoted as BSxSTN (x = 0, 0.25 and 0.5), were synthesized by the conventional solid-state reactions route. The impact of Sr-substitution in Ba2SmTi2Nb3O15 ceramics on their structural, optical, and dielectric properties are investigated. The Rietveld method was employed to confirm the formation of tetragonal tungsten bronze with the P4bm space group, using X-ray diffraction data. The substitution of Ba by Sr resulted in a decrease in cell parameters, density, and the average crystallite size as determined by Scherrer's formula ranged from 29.4 to 32 nm. The compounds frequency-dependent dielectric properties were studied using complex impedance spectroscopy over a temperature range of 50 to 420 °C at different frequencies. Dielectric measurements revealed a high dielectric constant, and the compounds exhibited characteristics of diffuse ferroelectric behavior. As the Sr content increased, optical gap energy increases from 3.29 to 3.59 eV, diffusivity increased from 1.19 to 1.52, Curie temperature (Tc) decreased from 269 to 213 °C, and the dielectric loss at room temperature and 1 kHz significantly decreased from 3 × 10-3 to 7 × 10-4. The correlation between (Tc) and the off-center cationic displacement of Ti/Nb in the octahedral Ti/NbO6 was analyzed. Cole-Cole plots for each sample displayed a single semicircular arc, indicating the presence of a single relaxation process.

Effects of W/Co co-doping on the structural, multiferroic, dielectric and optical properties of filled tungsten bronze Ba4Sm2Fe2Nb8O30 ceramics

The structural, magnetic, ferroelectric, dielectric, magneto-dielectric and optical properties of W/Co co-substituted tungsten bronze Ba4Sm2Fe2Nb8-3x(W2Co)xO30 (0 ≤ x ≤ 0.3) ceramics were studied in detail. All the samples can be indexed with the tetragonal structure with the space group of P4bm. The room-temperature ferromagnetism with rather high ferromagnetic Curie temperature Tc was obtained in all compositions. The co-doping of W/Co ions obviously optimized the ferromagnetism and ferroelectricity. The composition x = 0.2 showed a superior multiferroicity with the remnant magnetization Mr of 0.15 emu/g and the remnant polarization Pr of 2.1μC/cm2 as well as the Tc of 886 K. The low-temperature relaxation was related to the thermal process of oxygen vacancies, while the another one around 300 K was ascribed to the localized hopping of electrons. The relative increment of magneto-dielectric constant (MDC) obeyed with the square term of magnetization in Ginzburg-Landau theory, implying the existence of intrinsic magneto-electric coupling effect. A relatively large MDC of 0.17 % was achieved in pure sample. In addition, two direct inter-band transitions with the narrow band gaps of ∼2.0 eV and ∼2.5 eV were demonstrated.

Synthesis and characterization of (Ba (1.6-3/2X) Sr2.4Na2Nb10O30: xHo3+) ferroelectric nanomaterials by solid state reaction routes for device applications

Barium Strontium Sodium Niobate (Ba (1.6-3/2X)Sr2.4Na2Nb10O30:xHo3+) tungsten bronze structured ferroelectrics nanomaterial synthesized by conventional solid state reaction route is investigated. The X-ray diffraction (XRD), the scanning electron spectroscopy (SEM), energy dispersive x-ray spectroscopy (EDS), Fourier transform-infrared spectroscopy (FTIR) and UV–Vis Spectroscopy were used to study the structure, surface morphology/microstructure, elemental composition/mapping, functional groups identification and absorption, respectively. The XRD pattern revealed Tetragonal Tungsten Bronze structured crystallite phase that matches with the JCPDS card number -00-039-1453 having space group of p4bm and lattice parameters of a = 12.33 Å, b = 12.33 Å and c = 3.93 Å. The average crystallite size of the synthesized samples obtained at the prominent peak (311) for position/2ϴ = 32.320 is 67.52 nm. The SEM images showed that surface microstructures have random and nearly uniform distribution of nanoparticles with different shapes and size on the surface. Moreover, less porous surface microstructure was obtained and it is promising for enhancing ferroelectric properties. EDS analysis confirmed the presence of all the constituent elements with their proportional atomic and molecular weight ratios. For the pure metal oxide, the FTIR results showed the bond vibration mode at wavenumber of 540.60 cm−1, having only single collective metal oxide intense peak without impurities. For Ho3+ concentration corresponding to 0.05 and 0.10 %, additional peaks were observed at 429.92 cm−1 and 415.77 cm−1, respectively, confirming the existence of Ho–O bond vibration modes. The UV–vis results show that the absorption edges of all samples are at the same wavelength region (approximately 205 nm). Moreover, it was observed that the optimum absorption intensity was obtained for 0.03 % Ho3+ ions concentration.

Crystallographic, Structural, and Electrical Properties of W6+ Substituted with Mo6+ in Crystalline Phases such as TTB Structure

Owing to their low dielectric loss and high permittivity values, dielectric ceramics have garnered a lot of interest from the scientific and industrial sectors. These properties allow for their downsizing and use in a variety of electronic circuits. This present work focuses on the impact of the substitution of W6+ with Mo6+ on the structural and dielectric features of the crystalline phases in a similar TTB structure within the Ba0.54Na0.46Nb1.29W(0.37−x)MoxO5 system, with 0 ≤ x ≤ 0.33 mol%. These crystalline phases were elaborated using the conventional solid-state reaction method and analyzed with XRD, Raman, and dielectric techniques. The Rietveld refinement method showed that all these phases are characterized by tetragonal structure and the P4bm space group. The Raman spectra corresponded well to a TTB-like structure, and all the bands were assigned. The dielectric measurements of the prepared ceramic samples facilitated the determination of their phase transition temperature (Tc) and the dielectric responses. This investigation focused on determining dielectric permittivity (ε′) and its correlation with increases in MoO3 content in the ceramic structure.

Refinement of the crystal structure of fresnoite, Ba2TiSi2O8, from Löhley (Eifel district, Germany); Gladstone-Dale compatibility, electronic polarizability and vibrational spectroscopy of minerals and inorganic compounds with pentacoordinated TiIV and a titanyl bond.

Most known compounds with five-coordinated Ti4+ are natural and synthetic titanosilicates. The crystal structure of natural fresnoite, Ba2TiSi2O8 [tetragonal, space group P4bm, a = 8.510 (1) Å, c = 5.197 (1) Å, V = 376.4 (1) Å3, Z = 2], has been refined to R = 0.011 on the basis of 807 unique single-crystal reflections with I > 2σ(I). Titanium has fivefold coordination with one short (`titanyl') bond of 1.692 (5) Å. Bonds in the TiO5 polyhedron are discussed in comparison to analogous coordination polyhedra in other minerals and compounds. A review of all known compounds with Ti4+O5 polyhedra shows that most of them are titanosilicates in which titanium forms a short Ti-O bond (∼1.61 to ∼1.77 Å). Poor Gladstone-Dale compatibility between chemical composition, optical characteristics and density of these compounds is explained by the anomalous contribution of [5]Ti4+ to the optical properties as shown by calculations based on the relationship between electronic polarizabilities and refractive indices. An improved Gladstone-Dale coefficient of 0.29 is suggested for TiO2 with [5]Ti4+. A negative correlation between `titanyl' bond lengths and wavenumbers of the bands of Ti-O stretching vibrations (in the range of 890-830 cm-1) in infrared and Raman spectra is observed.

Synthesis and structural studies of lead-free (Na0.5Bi0.5)0.92Ba0.08TiO3 - Co0.6Zn0.4Fe1.7Mn0.3O4 magnetoelectric composites

Two phase Lead-free magnetoelectric composites with the formula (1-x) (Na0.5Bi0.5)0.92Ba0.08TiO3-(x) Co0.6Zn0.4Fe1.7Mn0.3O4 [(1-x) NBBT-xCZFMO] (where x = 0, 0.2, 0.4, 0.5, 0.6, 0.8 and 1 mol%) have been synthesized through conventional solid-state reaction method. X-ray diffraction (XRD) and Scanning electron microscopy (SEM) methods have been employed for structural and morphology studies on the synthesized samples. XRD and SEM studies revealed that the single-phase synthesis of NBBT & CZFMO and the existence of both the parent phases in the composites. Here, ferroelectric NBBT formed in tetragonal crystal structure with P4bm space group, whereas ferrite CZFMO crystallized in Cubic structure with Fd-3m space group. Raman spectroscopy is also carried out on all the synthesized samples. In case of NBBT six Raman active modes are observed between wave numbers from 100 cm−1 to 1000 cm−1 and in accord with the earlier reports. Whereas, when it comes to CZFMO, five modes are observed in the region of 100 cm−1 to 1000 cm−1 at 162 cm−1, 309 cm−1, 472 cm−1, 620 cm−1 and 690 cm−1. The composites contain the Raman peaks of both NBBT and CZFMO. The shifting of the Raman peaks observed in the composites indicates the presence of strain at the interface of NBBT and CZFMO phases. The results are discussed in detail.

Rietveld Refinement, Structural Characterization, and Methylene Blue Adsorption of the New Compound Ba0.54Na0.46Nb1.29W0.37O5

Using the solid-state process, the new compound Ba0.54Na0.46Nb1.29W0.37O5 was effectively produced in a single crystalline phase. The material’s characteristics were determined by X-ray diffraction and Raman techniques. The Rietveld method was applied to refine the structural properties of this sample using X-ray diffraction data and derive the diffraction line profile. The cell parameters a = b = 12.37843 ± 0.02 and c = 3.93526 ± 0.02 were accustomed to crystallizing this compound in the tetragonal tungsten bronze (TTB) structure of the space group P4bm. Thanks to Raman measurements, we were able to detect numerous vibration modes in this crystalline phase. The adsorption of methylene blue (MB) on crystalline phase was studied by UV–visible spectroscopy. On account of methylene blue adsorption on Ba0.54Na0.46Nb1.29W0.37O5, it was discovered that this material can be used to remove organic pollutants and thus be used for water treatment.

Effect of B-site Zr and Hf substitution on ferroelectric polar order for tetragonal tungsten bronze ceramic

ABSTRACT Lead free ferroelectric ceramic Ba4Sm2Hf4Nb6O30(BSHN) with tungsten bronze structure was synthesized and characterized. The effect of B-site cation electron configuration (Hf and Zr) on origin of ferroelectricity and polarization reversal was also studied in detail. The X-ray diffraction (XRD) pattern was indexed with tetragonal tungsten bronze in P4bm space group for BSHN. Obvious dielectric anomaly was observed in the temperature dependent permittivity curve, and quite large thermal hysteresis was obtained from the differential scanning calorimetry (DSC) result. While at lower temperature (<T C), there are two distinct dielectric relaxations for BSHN, respectively related to the activation of frozen polar region and activation of the fully free reversal for the polarization. Compared with Ba4Sm2Zr4Nb6O30(BSZN), Hf substitution in B site makes it harder to activate the frozen polar nanoregion but easier to realize free polarization reversal. This could be further confirmed by the measured polarization-electric field (P-E) curve. Meanwhile, the Raman modes intensity showed gradual change rather than abrupt one for BSHN when the temperature increased through the Curie point, which was quite different from the Zr based compounds. The difference in BO6 octahedral tilting, B-site cation’s electron configuration and B-O bond character are the main cause of these distinct dielectric and ferroelectric property.

Investigation of tungsten bronze ferroelectric ceramic by conventional and mechanical activation processes

In the present work, the nanocrystalline tungsten bronze ferroelectric ceramics of composition Ba5CaTi2Nb8O3o were synthesized by high energy ball milling successfully and compared with conventional solid-state reaction technique for improved applications. The synthesized samples were characterized by using X-ray diffraction, EDAX, scanning electron microscope, and transmission electron microscope. X-ray analysis confirms single-phase tetragonal structure by JCPDS card 039–0258 with space group P4bm. Transmission electron microscopy reveals particle size reduced to nano-range by mechanical activation in comparison with the conventional solid-state process.

Large piezoelectricity in NaNbO3-based lead-free ceramics via tuning oxygen octahedral tilt.

The development of high-performance lead-free piezoceramics for replacing Pb-based perovskites has attracted lots of attention, and comparable room-temperature piezoresponse has been realized in (Na,K)NbO3 and BaTiO3-based ceramics with local structure heterogeneity via adjusting polymorphic phase boundary. In this work, a new method of oxygen octahedron tilt design is used in NaNbO3-based lead-free ceramics, which usually shows complex oxygen octahedron tilt information inherited from NaNbO3. The substitution of Ba(Fe0.5Nb0.5)O3 and BaTiO3 with high tolerance factor into NaNbO3 leads to a gradual elimination of anti-parallel cation displacement and anti-phase tilt along the three axes; as a result, a single tetragonal phase with P4bm space group and only in-phase tilt along c axis is achieved in 0.88NaNbO3-0.04Ba(Fe0.5Nb0.5)O3-0.08BaTiO3 ceramic. Accompanying the decreased oxygen octahedral tilt degree, a drastically improved d33 up to 367 pC N-1 (over ten times that of NaNbO3 ceramic) is obtained, reaching a record high in NaNbO3-based lead-free ceramics. Together with temperature insensitive piezoresponse originating from thermally stable oxygen octahedral tilt structure, the studied NaNbO3-based materials show large potential for replacing Pb-based ceramics in some electronic devices. The oxygen octahedron tilt engineering would be used for designing more high-performance lead-free ceramics with high piezoresponse and excellent thermal stability simultaneously.

Structures and phase transitions in barium sodium niobate tungsten bronze (BNN)

The room-temperature structure of the filled tetragonal tungsten bronze, Ba2NaNb5O15 (BNN), has been the subject of a number of studies, and these studies have given an almost corresponding number of different results. From a group theoretical examination of the different possibilities and a review of the published experimental results we conclude that the room-temperature structure is that proposed by Labbé et al. [J. Phys. Condens. Matter (1989), 2, 25–43] in the space group Bbm2 (Ama2 in standard setting) on a 2\sqrt{2}a × \sqrt{2}a × 2c cell. Upon heating, the structure remains ferroelectric but becomes tetragonal (space group P4bm) at 550 K, then paraelectric (space group P4/mbm) at and above 860 K.

Structural and impedance spectroscopic study of Zn-substituted Ba5CaTi2Nb8O30 tetragonal tungsten bronze ceramics

Zn-doped tungsten bronze compounds derived from Ba5CaTi2Nb8O30, with Ba5CaTi2−xZnxNb8O30 composition (x = 0; 0.04 and 0.08) were synthesized by the conventional solid-state reaction route. Both solubility of Zn in Ba5CaTi2Nb8O30 and tungsten bronze formation with the P4bm space group were verified by the Rietveld method using X-ray diffraction data. The average crystallite size was of the order of 0.08 µm according to Scherrer's formula. SEM micrographs of Ba5CaTi2−xZnxNb8O30 ceramics showed high densification, low porosity, thus a homogeneous grain distribution of different sizes over the entire surface. The average grain size was in the range of 1.3–1.6 µm. The frequency-dependent electrical properties were analyzed by complex impedance spectroscopy. Different types of studies such as the Nyquist plot, real and imaginary part of the impedance, conductivity, modulus formalism, and charge carrier activation energy were used to explain the microstructure-electrical properties relationships.

Structural, dielectric and energy storage properties of Neodymium niobate with tetragonal tungsten bronze structure

The present work reports the effect of Nd3+ substitution on the structural, dielectric and energy storage properties of the polycrystalline Ba2NaNb5O15(BNN) ceramics. The ferroelectric lead-free Ba2Na1-xNdx/3Nb5O15 ceramics were prepared by conventional solid-state reaction technique. The room temperature X-ray study and Raman spectroscopy investigations have allowed evidencing the stabilization of a tetragonal tungsten bronze structure with P4bm space group for all the studied compounds. Dielectric study carried out on the prepared ceramics has permitted to determine the temperature of phase transitions (Tc). It was found that the dielectric constant increased with increasing the amount of Nd in BNN matrix. Room temperature energy storage property was determined using P-E hysteresis loops. The optimum discharge density was found for the composition x = 0.7 with Wrec = 18.1 mJ cm−3) at 1 Hz. Finally, the dynamic of phase transition was approached using thermal Raman spectroscopy investigations.

Dielectric and optical spectroscopy of new polycrystalline ceramic for device applications

The polycrystalline double perovskite Li2GdFeTiO6 was synthesized through the solid-state mixed oxide method and its preliminary crystal structure was investigated by the XRD technique. The structure of the material was identified to be tetragonal with space group P4bm using POWD and MATCH software. The morphology of the sample was investigated through a scanning electron microscope (SEM) and the average grain size was found to be 3.82 μm using the intercept technique. The investigation of the perovskite phase and various vibrational modes were carried out through FTIR spectroscopic technique. The bandgap (Eg = 1.73 eV) and visible light sensitivity of the material were identified by UV–Visible spectroscopic operation carried in the range 200–700 nm. The dielectric and related properties were investigated as a function of frequency and temperature using an impedance analyzer (LCR meter). Room-temperature dielectric investigation suggests it may be useful for storage application. The transport activities investigated through conductivity, impedance, and modulus technique illustrate the significant influence of grains on transportation of charges.

Bennesherite, Ba2Fe2+Si2O7: A new melilite group mineral from the Hatrurim Basin, Negev Desert, Israel

AbstractThe first barium member of the melilite group, bennesherite Ba2Fe2+Si2O7 [P421m, Z = 2, a = 8.2334(14) Å, c = 5.2854(8) Å, V = 359.29(13) Å3], was discovered in thin veins of rankinite paralava within pyrometamorphic gehlenite hornfels at Gurim Anticline, Hatrurim Basin, Negev Desert, Israel. Bennesherite occurs in small intergranular spaces between large crystals of rankinite, gehlenite, and garnet together with other Ba-minerals such as fresnoite, walstromite, zadovite, gurimite, hexacelsian, and celsian. It forms transparent, light yellow to lemon-colored crystals with a white streak and a vitreous luster. They exhibit good cleavage on (001), a brittle tenacity, and a conchoidal fracture. The estimated Mohs hardness is 5. Bennesherite has a melilite-type structure with the layers composed of disilicate (Si2O7)6− groups and (Fe2+O4)6− tetrahedra, connected by large eightfold-coordinated Ba atoms. In some grains, epitaxial intergrowths of bennesherite and fresnoite are observed. The structure of the fresnoite, Ba2TiO(Si2O7) with a P4bm space group and unit-cell parameters a = 8.5262(5) Å, c = 5.2199(4) Å, is closely related to the structure of bennesherite. Among all the known minerals of the melilite group, bennesherite has a structure characterized by the lowest misfit degree between the tetrahedral (T1 and T2 sites) and polyhedral (X-site) layers, as it was shown in both natural and synthetic melilite-type phases.

Crossover from normal to relaxor ferroelectric in Sr0.25Ba0.75(Nb1−xTax)2O6 ceramics with tungsten bronze structure

The crossover from normal to relaxor ferroelectrics in Sr0.25Ba0.75(Nb1−xTax)2O6 (x = 0, 0.1, 0.25, and 0.5) ceramics was determined together with the structure evolution. A single-phase tungsten bronze structure in space group P4bm (x = 0 and 0.1) or P4/mbm (x = 0.25 and 0.5) was obtained in the entire composition range. The lattice parameter a increased, while c, tetragonality c/a, and cell volume decreased with increasing x. Meanwhile, the dielectric maximum temperature Tm went down and the dielectric peak exhibited an enhanced diffused nature with a stronger frequency dispersion, where the saturated P–E loop (x = 0 and 0.1) transformed to a slim relaxor loop (x = 0.25) and finally to the linear one (x = 0.5). Raman spectra results revealed the reduced covalence between the B-site cation and the oxygen ion as a result of Ta-substitution. The coexistence of Nb5+ and Ta5+, which possessed the distinct covalence with the oxygen ion, played the key role in the structural variation and crossover from normal to relaxor ferroelectrics in the present system.