Space Group Amm2 Research Articles

Crystal structure and properties of perovskite-type rubidium niobate, a high-pressure phase of RbNbO3.

We synthesized a perovskite-type RbNbO3 at 1173 K and 4 GPa from non-perovskite RbNbO3 and investigated its crystal structure and properties towards ferroelectric material design. Single-crystal X-ray diffraction analysis revealed an orthorhombic cell in the perovskite-type structure (space group Amm2, no. 38) with a = 3.9937(2) Å, b = 5.8217(3) Å, and c = 5.8647(2) Å. This non-centrosymmetric space group is the same as the ferroelectric BaTiO3 and KNbO3 but with enhanced distortion. Structural transition from orthorhombic to two successive tetragonal phases (Tetra1 at 493 K, Tetra2 at 573 K) was observed, maintaining the perovskite framework before reverting to the triclinic ambient phase at 693 K, with no structural changes between 4 and 300 K. The first transition is similar to that of KNbO3, whereas the second to Tetra2, marked by c-axis elongation and a significant cp/ap ratio jump (from 1.07 to 1.43), is unique. This distortion suggests a transition similar to that of PbVO3, where an octahedron's oxygen separates along the c-axis, forming a pyramid. Ab initio calculations simulating negative pressure like thermal expansion predicted this phase transition (cp/ap = 1.47 at -1.2 GPa), aligning with experimental findings. Thermal analysis revealed two endothermic peaks, with the second transition entailing a greater enthalpy change and volume alteration. Strong second harmonic generation signals were observed across Ortho, Tetra1, and Tetra2 phases, similar to BaTiO3 and KNbO3. Permittivity increased during the first transition, although the second transition's effects were limited by thermal expansion-induced bulk sample collapse. Perovskite-type RbNbO3 emerges as a promising ferroelectric material.

Analysis of amplitude and frequency-dependent scaling behavior of dynamic hysteresis loop and thermal properties of BaZr0.05Ti0.95O3 ceramic

In this work, single-phase BaZr0.05Ti0.95O3 (BZT) ceramic was prepared through a conventional solid-state reaction route. The structural identity was analyzed by X-ray diffraction (XRD) and Rietveld refinement, which reveals the single-phase perovskite structure of the synthesized sample having an orthorhombic structure and space group Amm2. Scanning electron microscope (SEM) study gives an idea about the well-dense grains with clear grain boundaries of the BZT sample. Frequency and amplitude-dependent Polarization-Electric field (P-E) and Strain-Electric field (S-E) loops were studied. The parameters like remnant polarization (Ec), coercive field (Pr), loop area (<A>), energy storage efficiency (η), field-induced maximum strain (Smax) and inverse piezoelectric coefficient (d33*) were calculated. The scaling behavior of the hysteresis loops area as a function of frequency and field strength is studied. The thermal conductivity and thermal diffusivity as a function of temperature were investigated.

Synthesis, crystal structure, and photoluminescence of new strontium barium nitrido-alumino-silicate phosphor, Sr27.9Ba22.8Al61.4Si174.6N328.4:Eu2+

Single crystals of a new nitrido-alumino-silicate containing both Sr and Ba, Sr27.9Ba22.8Al61.4Si174.6N328.4:Eu2+, were synthesized by heating a binary-nitride powder mixture at 2030 °C under a N2 gas pressure of 0.85 MPa for 4 h. The fundamental X-ray diffraction spots were indexed using orthorhombic cell parameters (a = 19.0272(5) Å, b = 40.4608(10) Å, c = 9.8641(3) Å), and diffuse streaks were observed between these spots. The crystal structure was analyzed using a statistical average structure model with space group Amm2. The (Al/Si)N4 tetrahedra share vertex and edge N atoms to form a three-dimensional network structure. Sr, Ba, and Eu atoms are distributed in the spaces within the network. Single crystals of Sr27.9Ba22.8Al61.4Si174.6N328.4:Eu2+ excited by light with a wavelength of 400 nm emitted yellow–orange light and showed a broad emission spectrum with a peak at 684 nm and a peak full-width at half-maximum of 239 nm. The maximum emission intensity at 200 °C was 74% of that at 25 °C.

Intermetallics La4M3Al3 and La4M5Al2 (M = Co, Ni) with M/Al slabs as building blocks

New compounds were obtained by arc-melting and characterized by X-ray diffraction on single crystal or on powder sample. The compounds crystallize with own types of structure: iso-structural La4Co3Al3 and La4Ni3Al3 with non-centrosymmetric space group Amm2 and Z ​= ​2 (a ​= ​4.148(5), b ​= ​10.111(7), c ​= ​10.601(7) Å for La4Co3Al3 and a ​= ​4.1895(7), b ​= ​10.0465(15), c ​= ​10.6538(16) Å for La4Ni3Al3). In contrast, iso-stoichiometric La4Co5Al2 and La4Ni5Al2 are not iso-structural. La4Co5Al2 crystallizes in space group Pnnm, Z ​= ​2, a ​= ​8.2997(11), b ​= ​13.5982(15), c ​= ​4.1160(6) Å. La4Ni5Al2 adopts a site exchange variant of Ca4Ni4Ge3 structure: Cmcm, Z ​= ​4, a ​= ​4.1848(6), b ​= ​10.3177(13), c ​= ​21.033(2) Å. Structural peculiarity of all the compounds are infinite corrugated M/Al layers between which La atoms are situated.

Analytical study of the ferroelectric properties of Fe-doped KNbO3 single crystal

We report herein the structural, dielectric, ferroelectric, and domain properties of an Fe-doped potassium niobate ([KNbO3] KNb1-xFexO3; x = 0.01 mol%) single crystal synthesized by a flux method. X-ray diffraction (XRD) results illustrate that the given sample adopts orthorhombic crystal symmetry with the space group Amm2. On submitting the sample to differential thermal analysis (DTA), two endothermic peaks were observed, the first at 224 °C and the second at 425 °C. Dielectric studies with respect to temperature from 30 to 500 °C showed that the Curie temperature (Tc) of the Fe-doped KNbO3 single crystal occurred at 435 °C. The measured dielectric loss of the crystal is in good agreement with other dielectric studies. The relationship between polarization and electric field (PE) shows that the spontaneous polarization (Ps) and coercive field (Vc) for the doped material are lower than those for an undoped KNbO3 single crystal, indicating a weakly ferroelectric nature of the sample. A trinocular microscope has been used to study the domain properties and revealed the formation of 60° and 90° domain walls. Furthermore, upon etching the single crystal with nitric acid (HNO3), etch pits and a twinning plane of the domains were formed. Finally, electric fields of 100, 500, and 1000 V/cm were applied to the Fe-doped KNbO3 single crystal surface, whereupon the nucleation and dissipation of new domains could be observed.

Room-temperature ferromagnetism in (K0.5Na0.5)NbO3-xBaNi0.5Nb0.5O3-δ ferroelectric ceramics with narrow bandgap

In this paper, a simple, reproducible and cost-effective solid-state reaction sintering process is developed to fabricate (K0.5Na0.5)NbO3-xBaNi0.5Nb0.5O3-δ (KNN-xBNN) ceramics with a narrow bandgap and room-temperature ferromagnetism. Here, we report a systematic investigation of the influence of the BaNi0.5Nb0.5O3-δ (BNN) concentration on the properties of KNN-xBNN ceramics. All ceramics form orthorhombic perovskite structures with a space group Amm2 and a weak peak at the wavelength of 550 cm−1 that is characteristic of the pillow shoulder of the orthorhombic phase. KNN-xBNN ceramics with x between 0.02 and 0.08 have a narrow bandgap of about 2.5 eV—much smaller than the 3.5 eV of its parent (K0.5Na0.5)NbO3 (KNN) ceramic—which is attributed to Ni2+-oxygen vacancy combinations (Ni2+-VO) raising the valence electron energy level of the KNN ceramic. Furthermore, doping BNN into KNN ceramics can significantly convert the magnetism from diamagnetism to ferromagnetism and the component of x = 0.08 achieves both maximum saturation magnetisation intensity (14 memu/g) and minimum coercive magnetic field (80 Oe). Our findings provide a systematic insight into the bandgap tunability and ferromagnetism induction at room temperature in lead-free perovskite KNN-xBNN ceramics, as well as demonstrate their potential applications in perovskite solar cells and multiferroic devices.

A new rare-earth borate Na3-3δEu2+δ(BO3)3 (δ = 0.16): Synthesis, crystal structure, vibrational spectra, and luminescent properties

A new rare-earth borate Na3-3δEu2+δ(BO3)3 (δ = 0.16) has been prepared using a high temperature flux method and structurally characterized by single-crystal X-ray diffraction analyses. The compound crystallizes in the orthorhombic space group Amm2 with a = 5.08902 (11) Å, b = 10.9754 (2) Å, c = 7.01996 (14) Å, V = 392.094 (14) Å3, and Z = 2. It features a three-dimensional framework constructed by interconnecting NaO6, EuO9, (Na/Eu)O8 distorted polyhedra, and BO3 planar triangles. Furthermore, IR, Raman, XPS, and UV–vis absorption spectra as well as photoluminescence properties of this compound were studied. Under near-UV excitation (396 nm), Na3-3δEu2+δ(BO3)3 (δ = 0.16) exhibits an intense reddish-orange emission centered at around 614 nm with the CIE coordinates of (0.637, 0.363), which can be assigned to the electric dipole 5D0→7F2 transition of Eu3+ ions. The phosphor shows the stable luminescence and color purity at elevated temperature. We may expect it to be a potential reddish-orange phosphor pumped by near-UV LED chips.

Demagistrisite, the Missing Link in a Polysomatic Series from Lawsonite to Orientite

Abstract Demagistrisite, ideally BaCa2Mn3+4(Si3O10)(Si2O7)(OH)4·3H2O, is a new mineral found at the Cerchiara mine (eastern Liguria, La Spezia province, Italy). The ore consists of rhythmic interlaying of braunite-bearing metasediments (5–15 cm thick) and hematite-rich cherts. Demagistrisite occurs in association with cerchiaraite-(Mn), namansilite, noelbensonite, orientite, richterite, ruizite, and saponite in matrix consisting of braunite, calcite, cryptomelane, orthoclase, and quartz. Demagistrisite crystals occur as tightly intergrown blades or as millimeter-sized prisms and needles with square cross-section, typically with irregular terminations, and rarely terminated by a low-angle pyramid. The mineral is orange brown to red brown, streak is beige, and luster is vitreous, translucent to transparent. Fracture is irregular. In thin section, it is orange brown. The mineral is optically biaxial (–) with α 1.805(5), β 1.825(5), γ 1.8305(5) (white light); 2Vmeas 58(5)°, 2Vcalc 54.7°; optical orientation X = c, Y = b, Z = a. Dispersion is very strong, r &amp;gt; v. Pleochroism is strong with X orange yellow, Y red brown, Z red brown; X &amp;lt;&amp;lt; Z &amp;lt; Y. It is unreactive in concentrated HCl at room temperature. Thirteen chemical analyses by WDS-EMPA gave the following empirical formula (based on 24 O apfu): (Ba0.69Ca1.25Mn2+0.70Sr0.21Na0.12Mg0.02)Σ2.99(Mn3+3.97Al0.03)Σ4(Si3O10)(Si2O7)(OH)3.87·3.13H2O. The mineral is orthorhombic, space group Amm2, with unit-cell parameters a 16.312(8), b 6.176(4), c 9.075(6) Å, V 914.2(10) Å3, and Z = 2. The seven strongest X-ray powder diffraction lines are [d Å (I%; hkl)]: 16.21 (49; 100), 4.86 (44; 111), 4.34 (56; 102,211), 2.871 (54; 220), 2.731 (100; 511,013), 2.671 (74; 320,113,502), and 2.426 (51; 222,313,611). The crystal structure (R1 = 0.0572 for 1485 reflections with I &amp;gt; 2σI) is based on straight edge-sharing chains of Mn3+-centered octahedra extending along [010], which are bridged by disilicate (Si2O7) and trisilicate (Si3O10) groups, yielding a framework. Cavities within this framework contain two large cation sites. The structure of demagistrisite can be considered transitional between the structures of orientite and noelbensonite. Demagistrisite is named in honor of Leandro de Magistris (1906–1990).

Phase composition of ceramic samples of the BaTiO3–PbTiO3–BaZrO3 system near BaTiO3

Ceramics (1 − x) Ba(Ti1 – yZry)O3·xPbTiO3 with x = 0, y = 0; x = 0, y = 0.05; x = 0.05, y = 0.05; x = 0.10, y = 0.05; x = 0.15, y = 0.05; x = 0.20, y = 0.05 were obtained by solid-state mixed oxide method at 1400 °C. Phase composition of the ceramic samples was determined by the Rietveld method using powder diffraction data. At the first stage, the refinement was done for the two most representative sections of the registered XRD patterns, namely: 2θ = 44.6 °–46.2 ° and 2θ = 55.4 °–57.2 °. At the second stage, the refinement for the full XRD patterns was performed. The quantitative content of phases and their crystallographic data is determined. All samples contain a perovskite tetragonal phase (space group P4 mm). The cubic phase (space group Pm-3 m) is present in the samples with x = 0, y = 0; x = 0, y = 0.05; x = 0.05, y = 0.05; x = 0.10, y = 0.05. The orthorhombic phase (space group Amm2) is contained in the samples with x = 0, y = 0.05; x = 0.05, y = 0.05; x = 0.10, y = 0.05; x = 0.15, y = 0.05. Substitution of Ti for Zr in the tetragonal form of BaTiO3 reduces the tetragonal distortion of the unit cell. Substitution of Ba for Pb increases the tetragonal distortion of the unit cell.

Heat capacity and high temperature electrical transport properties of TbNiC2

The single phase polycrystalline TbNiC2 sample was obtained by annealing at 1073 K. The compound adopts structure of CeNiC2-type, confirmed by XRD Rietveld refinement: space group Amm2, a = 3.6000(2) Å, b = 4.5129(2) Å, c = 6.0563(3), RB(I) = 3.72%, Rp = 5.46%. The orthorhombic CeNiC2 crystal structure prototype is shown to be derived from the hexagonal AlB2 one (space group P6/mmm) following the Bärnighausen formalism via translationengleiche. Zero-field heat capacity measurements of TbNiC2 in the range of 1.9–300 K reveal Sommerfeld coefficient γ = 8(1) mJ mol−1 K−2, phonon coefficient β = 1.18(1)∙10−4 J mol−1 K−4 with the derived Debye temperature of ΘD ≈ 404 K and antiferromagnetic state below TN = 25 K with a spin-wave excitation gap of Δ = 26(2) K. The 4f-electron contribution to the magnetic entropy change indicates a doublet ground state for a non-Kramer's Tb3+ ion. Thermopower and electrical resistivity of TbNiC2 have been measured in the range of 310–855 K and reveal values characteristic for metallic systems. Seebeck coefficient decreases with increasing temperature approximately linearly in the all studied interval, and its sign changes from positive to negative one at ~660 K, whereby the electrical resistivity increases from 310 K reaching maximum at ~640 K and afterwards decreases slightly. Maximum power factor value of 27 μW m−1 K−2 has been observed at 310 K.

Crystal structures and elastic properties of Ti(Cu,Pt)2 and Ti(Cu,Pt)3 phases

Abstract This paper focused on the crystal structures of two new ternary phases, Ti(Cu,Pt)2 and Ti(Cu,Pt)3, which were studied by X-ray powder diffraction data using Rietveld method. Electron probe microanalysis was used for sample composition examination. Elastic properties of these phases were further measured by nano-indentation, and meanwhile calculated with first-principle (FP) calculations. It is found that the crystal structure of Ti(Cu,Pt)2 is of orthorhombic cell space group Amm2 (No. 38) with structural prototype of VAu2. The resolved structure of Ti(Cu,Pt)3 is of tetragonal AlPt3 type, belonging to the space group P4/mmm (No. 123). The nano-indentation measurement and FP calculations show that the elastic modulus of Ti(Cu,Pt)2 increases firstly then decreases with Pt content, whereas that of Ti(Cu,Pt)3 almost linearly increases with Pt content.

Nitridophosphate-Based Ultra-Narrow-Band Blue-Emitters: Luminescence Properties of AEP8 N14 :Eu2+ (AE=Ca, Sr, Ba).

The nitridophosphates AEP8N14 (AE=Ca, Sr, Ba) were synthesized at 4–5 GPa and 1050–1150 °C applying a 1000 t press with multianvil apparatus, following the azide route. The crystal structures of CaP8N14 and SrP8N14 are isotypic. The space group Cmcm was confirmed by powder X‐ray diffraction. The structure of BaP8N14 (space group Amm2) was elucidated by a combination of transmission electron microscopy and diffraction of microfocused synchrotron radiation. Phase purity was confirmed by Rietveld refinement. IR spectra are consistent with the structure models and the chemical compositions were confirmed by X‐ray spectroscopy. Luminescence properties of Eu2+‐doped samples were investigated upon excitation with UV to blue light. CaP8N14 (λ em=470 nm; fwhm=1380 cm−1) and SrP8N14 (λ em=440 nm; fwhm=1350 cm−1) can be classified as the first ultra‐narrow‐band blue‐emitting Eu2+‐doped nitridophosphates. BaP8N14 shows a notably broader blue emission (λ em=417/457 nm; fwhm=2075/3550 cm−1).

Enhanced pyroelectric figure of merits in Sr and Zr co-doped porous BaTiO3 ceramics

Porous Ba0.85Sr0.15Zr0.1Ti0.9O3 (BSZT + X wt% Poly-vinyl alcohol (PVA)) with X = 0, 5, 10, 15 ceramics were prepared by the conventional solid-state reaction method. Structural, dielectric, ferroelectric, and pyroelectric properties were systematically investigated with the increase in pore-forming agent PVA. X-ray diffraction (XRD) pattern shows co-existence of tetragonal and orthorhombic symmetries with space group P4mm and Amm2, respectively. Microstructure depicts the pore density in the ceramic samples increases with increase in PVA content. The temperature-dependent dielectric analysis illustrates that there is no change in Curie temperature (Tc ~ 327K) with the increase in PVA. Dielectric constant value decreases and dielectric loss increases with increase in PVA. The pyroelectric coefficient increases with the applied field and decreases with an increase in PVA. We observed strongly enhanced pyroelectric figure of merits (FOMs) with an increase in porosity content. At room temperature, porous BSZT ceramic sample (BSZT + 15 wt% PVA) exhibits a 29.17% increase in pyroelectric energy harvesting figure of merit Fe, 101.73% increase in energy harvesting figure of merit Fe*, 81.93% increase in voltage responsivity Fv, 10.95% increase in current responsivity Fi, 24.97% increase in detectivity-based FOM compared to dense ceramic sample. The enhancement in these FOMs is useful in the development of pyroelectric devices.

In situ synchrotron radiation investigation of V2O5-Nb2O5 metastable compounds: transformational kinetics at high temperatures with a new structural solution for the orthorhombic V4Nb20O60 phase.

Due to the considerable interest in vanadium niobium oxides as a lithium storage material, the kinetics and transformation processes of the V2O5-5Nb2O5 system have been investigated by in situ synchrotron powder X-ray diffraction. The diffraction data after the thermal treatments selected with a view on the most significant features were supplemented with specific ex situ experiments conducted using a laboratory rotating anode X-ray diffractometer. The morphological changes of the mixed powders assuming an amorphous and nanocrystalline solid solution structure as a function of the temperature were inspected by scanning electron microscopy observations. The structural solution of the powder diffraction pattern of the phase recorded in situ at a temperature of about 700 °C was compatible with an orthorhombic crystal structure with the space group Amm2. The obtained lattice parameters for this structure were a = 3.965 Å; b = 17.395 Å, c = 17.742 Å, and the cell composition was V4Nb20O60, Pearson symbol oA84, and density = 4.10 g cm-3. In this structure, while the niobium atoms may be four-, five-, and six-fold coordinated by oxygen atoms, the vanadium atoms were six-fold or seven-fold coordinated. At the temperature of 800 °C and just above, the selected 1 : 2 and 1 : 3 V2O5-Nb2O5 compositions, respectively, returned mostly a tetragonal VNb9O25 phase, in line with earlier observations conducted for determination of the stability phase diagram of such quasi-binary systems.

Syntheses and crystal structures of a new family of hybrid perovskites: C5H14N2·ABr3·0.5H2O (A = K, Rb, Cs).

The syntheses and crystal structures of three hybrid perovskites, viz. poly[1-methyl-piperizine-1,4-diium [tri-μ-bromido-potassium] hemihydrate], {(C5H14N2)[KBr3]·0.5H2O} n , (I), poly[1-methyl-piperizine-1,4-diium [tri-μ-bromido-rubidium] hemihydrate], {(C5H14N2)[RbBr3]·0.5H2O} n , (II), and poly[1-methyl-piperizine-1,4-diium [tri-μ-bromido-caesium] hemihydrate], {(C5H14N2)[CsBr3]·0.5H2O} n , (III), are described. These isostructural (space group Amm2) phases contain a three-dimensional, corner-sharing network of distorted ABr6 octa-hedra (A = K, Rb, Cs) with the same topology as the classical perovskite structure. The doubly protonated C5H14N2 2+ cations occupy inter-stices bounded by eight octa-hedra and the water mol-ecules lie in square sites bounded by four octa-hedra. N-H⋯Br, N-H⋯(Br,Br), N-H⋯O and O-H⋯Br hydrogen bonds consolidate the structures.

Dielectric and impedance spectroscopic study of lithium doped potassium tantalum niobium oxide

Abstract The (K0.90Li0.10) (Nb0.80Ta0.20)0.99Mn0.01O3 (KLTN) ceramic has been synthesized by the conventional solid-state reaction route. The Rietveld refinement X-Ray diffraction (XRD) patterns confirmed the single-phase orthorhombic crystal structure with space group Amm2. The frequency dependent electrical properties were examined by the complex dielectric and impedance spectroscopy in the temperature range 30 °C–500 °C where multiple structural phase transition was observed with high dielectric constant, low tangent loss and well saturated electric polarization. The shifting of the ferroelectric phase transition temperature by 30 °C in heating and cooling mode suggests the irreversible motion of the domains and domain walls and significant effects on grain boundaries on structural phase transition temperature. A series of phase transitions from orthorhombic to tetragonal (∼190 °C) and tetragonal to Cubic (∼390 °C in cooling and 420 °C in heating) have been obtained in the wide range of temperature. The different type of analogy such as Modulus formalism, complex impedance spectra, frequency dependent conductivity, the activation energy of charge carriers has been used to understand the microstructure-electrical properties relation.

Study on Structural, Ferroelectric, Piezoelectric and Dielectric Properties of Ba0.92Ca0.08TiO3-BaTi0.96Zr0.04O3 Lead-Free Electroceramics

ABSTRACTThe structural, ferroelectric, piezoelectric and dielectric properties of lead-free 0.45Ba0.92Ca0.08TiO3-0.55BaTi0.96Zr0.04O3 (BCT8-BZT4) ceramics synthesized by conventional solid state reaction method have been reported. Structural analyses by X-ray diffraction (XRD) and Raman spectroscopic measurements indicate that the BCT8-BZT4 ceramics possesses both tetragonal (space group P4mm) and orthorhombic (space group Amm2) crystal structures at room temperature. Dense microstructure with 5-7 µm grain size has been observed from scanning electron micrographs. Ferroelectric nature of BCT8-BZT4 has been confirmed from the polarization-electric field (P-E) hysteresis loop measurements. For BCT8-BZT4, the values of maximum polarization (Pmax=17.24 µC/cm2), remnant polarization (Pr=6.36 µC/cm2), coercive electric field (Ec=3.66 kV/cm) and direct piezoelectric coefficient (d33∼220 pC/N) have been observed to be comparable with those of lead based piezoelectric ceramics. The BCT8-BZT4 ceramics shows usual dielectric dispersion with dielectric constant ∼1210 above 100 kHz frequency at room temperature. The observed properties show that the BCT8-BZT4 ceramics is suitable for ferroelectric memory, piezoelectric sensor, capacitor, etc applications. Thus, it has been predicted that BCT8-BZT4 may be a potential candidate for replacing lead-based piezoelectric ceramics.

Influence of the anion nature on the properties of Sr-containing formamidinium tin halide perovskites

Abstract

Correlation between structural, ferroelectric, piezoelectric and dielectric properties of Ba0.7Ca0.3TiO3-xBaTi0.8Zr0.2O3 (x = 0.45, 0.55) ceramics

We report on the correlation between structural, ferroelectric, piezoelectric and dielectric properties of the (1-x)Ba0.7Ca0.3TiO3-xBaTi0.8Zr0.2O3 (x = 0.45, 0.55; abbreviated as 55BCT30 and 45BCT30) ceramics close to morphotropic phase boundary (MPB) region. The 55BCT30 and 45BCT30 ceramics were synthesized by the standard, high-temperature solid state ceramic method. X-ray diffraction (XRD) along with Rietveld refinement indicate that the 55BCT30 ceramics exhibit rhombohedral (R, space group R3m), orthorhombic (O, space group Amm2) and tetragonal (T, space group P4mm) phases while 45BCT30 ceramics exhibit only T and O phases. The temperature dependent Raman spectroscopy measurements confirm the structure and phase transformations observed from XRD. All the ceramics are chemically homogeneous and exhibit a dense microstructure with a grain size of 5–7 µm. The presence of polarization-electric field and strain-electric field hysteresis loops confirm the ferroelectric and piezoelectric nature of the ceramics. The polarization current density-electric field curves show the presence of two sharp peaks in opposite directions indicating the presence of two stable states with opposite polarity. Higher values of direct piezoelectric coefficient (d33 ~ 360 pC/N) were observed due to the existence of low energy barrier near MPB region and polymorphism. The 55BCT30 ceramics exhibit a higher value of electrostrictive coefficient (Q33 ~ 0.1339 m4/C2) compared to the well-known lead-based materials. The temperature dependent dielectric measurements indicate the O to T phase transition for 55BCT30 and 45BCT30. These ceramics exhibit a Curie temperature (Tc) of 380 K with a dielectric maximum of ~ 4500.

Structural, dielectric and magnetic properties of K0.5Na0.5NbO3 and K0.5 Na0.5Nb0.975Co0.025O3 lead free ceramics

ABSTRACTLead free ferroelectric ceramics of K0.5Na0.5NbO3(KNN) and K0.5Na0.5Nb0.975Co0.025O3(KNN-Co) have been synthesized by solid state reaction method. X-ray diffraction studies reveals that both pure and cobalt doped KNN ceramics exhibits orthorhombic structure belonging to the space group Amm2. Temperature dependent dielectric measurements shows an increase in Curie temperature (TC) for KNN-Co compared to KNN. Well saturated hysteresis loops have been obtained for both compositions from the P-E loop measurements. Further, magnetic behaviour of KNN and KNN-Co ceramics have been studied.