Two-step Solid-state Reaction Method Research Articles

Facile Preparation, Microstructure and Dielectric Properties of La(Cr0.2Mn0.2Fe0.2Co0.2Ni0.2)O3 Perovskite High-Entropy Ceramics

Preparation and properties of La(Cr0.2Mn0.2Fe0.2Co0.2Ni0.2)O3 high-entropy ceramics are investigated. La(Cr0.2Mn0.2Fe0.2Co0.2Ni0.2)O3 high-entropy ceramics are prepared by a traditional two-step solid-state reaction method in air. La(Cr0.2Mn0.2Fe0.2Co0.2Ni0.2)O3 single-phase powders are synthesized by calcining the mixed oxides at 1000 °C for 20 h. The high-entropy ceramics are sintered at 1350–1650 °C in a muffle furnace for 4 h by using the above powders. The phase compositions of the high-entropy ceramics at different temperatures are characterized by X-ray diffraction (XRD) with Cu Kα radiation. A field-emission scanning electron microscope with energy-dispersive spectroscopy (EDS) is used to observe the microstructures and analyze the elemental distributions. The hardness and dielectric properties are measured and discussed.

Impact of NiO nano-particles on colossal magneto-resistance of La0.70Ca0.30MnO3 composite

Mixed-valent perovskite manganite has gained considerable research interest due to the increasing demand for energy storage materials. Herein, we show that colossal magneto-resistance properties of La0.7Ca0.3MnO3 (LCMO) can be changed via nickel oxide (NiO) doping. A two-step conventional solid-state reaction method is used to synthesize LCMO-10% NiO composite. The phase purity, structural, electrical (resistivity), and magneto-transport properties of as-synthesized LCMO-10% NiO composite are detailed. NiO doping shifts metal–insulator transition temperature (TMI) from 263 K to 195 K and increases resistivity. The magneto-resistance (MR) measurements showed 10% NiO doping resulted in a maximum MR of ∼ -70.32% at 200 K (near TMI) and 10 T applied magnetic field. However, -0.0849% MR is seen at 290 K (RT) and 0.3 T. The increased ∼ -63.85% MR is found at 100 K and at 10 T, which is comparatively much higher than the pristine LCMO sample. This is due to the addition of NiO in LCMO that improves physical properties (i.e., grain size).

SnO2 modified PNN-PZT ceramics with ultra-high piezoelectric and dielectric properties

In this work, a two-step solid-state reaction method is used to prepare the 0.55 Pb(Ni1/3Nb2/3)O3-0.135PbZrO3-0.315PbTiO3/xSnO2 (PNN-PZT/xSnO2) ceramics. The influences of SnO2 on the crystalline structure, electromechanical properties, and temperature stability of PNN-PZT ceramics were studied in detail. The results demonstrate that the Sn4+ ions are successfully introduced into the PNN-PZT crystalline lattice and substitute B-site Ni2+ and Zr4+. The x = 0.0025 ceramic with the coexistence of rhombohedral, tetragonal, and pseudocubic phases exhibits the optimized comprehensive properties: the quasi-static piezoelectric constant d33, large-signal d33*, electromechanical coupling coefficients kp and kt, free dielectric constant εr, and mechanical quality factor Qm are 1123 pC/N, 1250 p.m./V, 0.63, 0.54, 9529, and 57, respectively. Meanwhile, the Curie temperature for this composition is 103 °C, almost maintaining the same level as the PNN-PZT matrix. After annealing at 75 °C, the retained d33 of x = 0.0025 ceramic is as high as 975 pC/N, superior to the PNN-PZT matrix (retained d33 ≈ 873 pC/N). Our results provide a promising piezoelectric material for board bandwidth, high sensitivity, and miniaturized medical ultrasonic transducers applications.

A correlative study between the microstructure and electrical properties of lead-free piezoceramics (1-x)BHT-xYLG driven by the synergistic action of multiple factors

Piezoceramics are important functional materials with broad applications in electronics, communication, medicine, and energy. Increasing environmental protection and human health concerns about the toxicity of lead have impelled the development of lead-free piezoceramics. At this work, in combination with phase field simulation, grain growth mechanism, ferroelectric domain wall model, and defect dipole formation mechanism, (1-x)Ba(Hf0.02Ti0.98)O3-x(Y0.5Li0.5)GeO3 [(1-x)BHT-xYLG, x = 0–0.40 mol%] lead-free piezoceramics were designed and fabricated via the two-step synthesis and solid-state reaction method, which yielded superior comprehensive electrical property. Phase field simulation respectively simulates the distribution of ferroelectric domains of O and T phase under different external electric fields (0–20 kV/mm) and the phase states under different temperatures (−100 to 150 °C). This research finds that their electrical properties are affected by the synergistic action of multiple factors, e.g., orthorhombic-tetragonal phase boundary (O-T PB), grain size (GS), domain-wall (DW), and defect dipole (DD), etc., rather than any single factor.

Influence of sintering temperature on the electrochemical properties of P2-type Na0.67Mn0.7Ni0.2Mg0.1O2 cathodes for sodium-ion batteries

Sodium-ion batteries are thought to be ideal alternatives to Lithium-ion batteries due to their similar electrochemical properties. However, several technique obstacles in cathode materials still impede the commercialized adoption of Sodium-ion batteries. Herein, the Mg-doping P2-type Na0.67Mn0.7Ni0.2Mg0.1O2 cathode materials were synthesized via a two-step process, including sol-gels and solid-state reaction method. This paper pays much attention to the optimal calcination temperature in the synthesis procedure and its effects are subsequently investigated. According to the results, under a series of calcination temperatures from 800 to 950 ​°C, Na0.67Mn0.7Ni0.2Mg0.1O2 cathode materials shows different particle sizes and crystalline structures, exhibiting varied electrochemical properties. Among them, samples calcinated at 900 ​°C display a high specific discharge capacity of 120.9 ​mAh g−1, and a stable cycling performance of 67.2% retention at 1 C rate for 100 cycles. The results suggest that calcination temperature at approximately 900 ​°C could effectively promote the electrochemical performance, which provides a good reference for the synthesis of cathode materials in sodium-ion batteries.

Effect of Ni and Fe substitution on the thermal, structural, vibrational spectroscopic and electrochemical properties of LiMn2O4 cathode material

Spinel LiMn2O4, Li1.025(Mn1.95Ni0.025Fe0.025)O4, and Li1.025(Mn1.9Ni0.025Fe0.05)O4 cathodes were synthesized by a two-step solid-state reaction method. The thermal, structural, vibrational spectra and electrochemical properties of these materials were characterized by using TGA-DTA, XRD, SEM, EDS, Fourier-FT-IR spectroscopy, Raman spectroscopy, and charge-discharge test. The TGA-DTA analysis confirmed that 800°C is the suitable temperature for synthesizing all the samples using Li2CO3, Fe2O3, MnO2, and NiO precursors. The XRD analysis revealed the formation of a single-phase cubic spinel structure with Fd3¯m space group. Two distinct strong absorption peaks were identified by FT-IR analysis in the wavenumber regions of 512 to 621 cm−1. Enhancement of the discharge specific capacity due to Ni and Fe substitution into LiMn2O4 was observed. Among all samples, Li1.025(Mn1.95Ni0.025Fe0.025)O4 exhibited excellent cyclic performance (97.4%) after 50 cycles.

Designing lead-free Barium Strontium Titanate-based weakly coupled relaxor ferroelectric ceramics with simultaneous high energy density and efficiency via Bi3+ lone pair covalent effect

Barium Strontium Titanate (Ba1-xSrxTiO3, BST) possesses the advantages of high permittivity, low remnant polarization and dielectric loss, suggesting great potential in the application of power capacitors. However, the low maximum polarization severely restricts the achievement of outstanding energy storage properties (ESP). Herein, we design a lead-free bulk ceramic: (1-x)Ba0.55Sr0·45TiO3-xBi0.5Na0.5TiO3 [(1-x)BST-xBNT] (x = 0.1–0.4), prepared by two-step solid-state reaction method. The introduction of BNT contributes to (1) the boost of maximum polarization (from 21 μC/cm2 up to 32.6 μC/cm2) due to Bi3+ lone pair covalent effect (2) strong relaxor behavior (1.71≪γ1.84) derived from weakly coupled nanopolar regions, which can be verified by high activation energy Ea = 0.341 eV at x = 0.3, improves the ESP and thermal stability of the ceramics. According to the above strategies, high Wrec = 1.73 J/cm3 and η = 84.4% are achieved in the 0.7BST-0.3BNT ceramics at 206 kV/cm, which is preferable to the previous results regarding BST-based bulk ceramics. The excellent thermal stability (20–120 °C), frequency stability (1–500 Hz), as well as anti-fatigue characteristic (cycling number: 105) were obtained in the 0.7BST-0.3BNT. Furthermore, 0.7BST-0.3BNT ceramics exhibit high-power density (PD = 44.9 MW/cm3) and rapid discharge rate (t0.9 = 99.2 ns) from 20 °C to 120 °C. This work provides a feasible way to achieve good energy storage and charge-discharge properties for pulse power energy storage systems.

MgPd2Sb : A Mg-based Heusler-type superconductor

We report the synthesis and physical properties of a full Heusler compound, MgPd$_2$Sb, which we found to show superconductivity below $T_c$ = 2.2 K. MgPd$_2$Sb was obtained by a two-step solid-state reaction method and its purity and cubic crystal structure (Fm-3m, a=6.4523(1) \r{A}) were confirmed by powder x-ray diffraction. Normal and superconducting states were studied by electrical resistivity, magnetic susceptibility, and heat capacity measurements. The results show that MgPd$_2$Sb is a type-II, weak coupling superconductor ($\lambda_{e-p}$ = 0.53). The observed pressure dependence of $T_c$ ($\Delta T_c / p \approx $ -0.23 K/GPa) is one of the strongest reported for a superconducting Heusler compound. The electronic structure, phonons, and electron-phonon coupling in MgPd$_2$Sb were theoretically investigated. The obtained results are in agreement with the experiment, confirming the electron-phonon coupling mechanism of superconductivity. We compare the superconducting parameters tothose of all reported Heusler-type superconductors.

Synthesis, Luminescent Properties and White LED Fabrication of Sm3+ Doped Lu2WMoO9

In this paper, Sm3+ doped Lu2W0.5Mo0.5O6, Lu2WMoO9, and Lu2(W0.5Mo0.5O4)3 materials were synthesized by using a two-step solid-state reaction method. The synthesized materials were characterized by X-ray diffraction (XRD) patterns, field emission scanning electronic micrograph (FE-SEM) pictures, photoluminescence (PL) excitation and emission spectra, and temperature-dependent emission intensities. Orange-reddish light could be observed from the phosphors under ultraviolet (UV) 365 nm light. The Sm3+ doped Lu2WMoO9 had enhanced PL intensities compared to the other two materials. The excitation, the energy transfer, the nonradiative relaxation, and the emission processes were illustrated by using schematic diagrams of Sm3+ in Lu2MoWO9. The optimal Sm3+ doping concentration was explored in the enhancing luminescence of Lu2WMoO9. By combing the Sm3+ doped Lu2WMoO9 to UV 365 nm chips, near white lighting emitting diode (W-LED) were obtained. The phosphor can be used in single phosphor-based UV W-LEDs.

Effect of Magnesium Doping to Reduce the Charge Reservoir Layer in Cu0.5Tl0.5(Ba2−xMgx)Ca2Cu3Oy (x = 0, 0.15, 0.25, 0.35) Superconductors

The charge reservoir layer plays a crucial role in the charge transfer mechanism in high-temperature superconductors. The effect of reducing the thickness of the Cu0.5Tl0.5Ba2O4−δ charge reservoir by replacing Ba with Mg atom in Cu0.5Tl0.5-1223 crystal has been studied. Cu0.5Tl0.5(Ba2−xMgx)Ca2Cu3Oy (x = 0, 0.15, 0.25, 0.35) superconductor samples were synthesized by a two-step solid-state reaction method. The as-grown samples showed orthorhombic crystal structure in which the c-axis lattice parameter and unit cell volume were systematically suppressed with increasing incorporation of Mg into the final compound, thereby resulting in suppression of the charge reservoir. The room-temperature resistivity increased with the Mg doping content, while the Tc and Tc-onset values decreased according to both resistivity and alternating-current (AC) susceptibility measurements. Fourier-transform infrared (FTIR) absorption measurements revealed three phonon modes related to vibrations of Tl–OA–Cu(2), Cu(1)–OA–Cu(2), and CuO2 planar oxygen atoms at around 420 cm−1, 480 cm−1 to 540 cm−1, and 580 cm−1, respectively. The apical oxygen mode of Tl–OA–Cu(2) type was hardened whereas the position of the latter two modes remained unchanged with increasing Mg doping in the final compound. Excess conductivity analyses showed a significant decrease in the onset temperature for Cooper pair formation (T*2D−SW). The coherence along the c-axis ξc(0), the interlayer coupling J, and the Fermi velocity vF of superconducting carriers increased with increasing Mg doping at Ba sites. These result suggest that the transfer mechanism of charge carriers from the Cu0.5Tl0.5Ba2O4−δ charge reservoir layer to the conducting CuO2 planes became more efficient, as evidenced by the increased coherence length ξc(0) and Fermi velocity vF of the carriers. However, the suppression of parameters such as Bc0(T), Bc1(T), Jc0(0), and τφ indicates that the density of pinning centers was suppressed with increasing Mg doping in the final compound.

Temperature Dependent Dielectric Properties of PB[(MG1/3NB2/3)1-XTIX]O3 for X= 0.25 Prepared By Solid State Reaction Method

Relaxor ferroelectric 0.75PMN-0.25PT was synthesized by two-step solid state reaction method via columbite route. The final mixed and grinded compositions was calcined at 9200C for 2h and then sintered at 12000C for 6h. The XRD data show the perovskite phase of prepared material with reduced pyrochlore phase and the SEM micrographs shows the compact and dense grains. The dielectric measurement shows the temperature dependent nature having dielectric constant 13189.44 at Curie temperature (Tc).

Concurrence of ferroelectric, dielectric and magnetic behaviour in Tb2Ti2O7 pyrochlore

We report the ferroelectric property in Tb2Ti2O7 pyrochlore, prepared by a two-step solid-state reaction method. A concave P-E (polarisation vs electric field) loop observed from 382 K confirms ferroelectricity, below which the loop remains as pointed or banana-shaped. Dielectric plots clearly show an anomaly at 383 K and the magnetic data reveals a deviation from 380 K supporting the observed ferroelectric ordering. The origin of ferroelectricity in Tb2Ti2O7 is discussed which is due to the structural distortion in TiO6 octahedron.

Weak ferromagnetism and magnetoelectric coupling through the spin–lattice coupling in (1−x)Pb(Fe2/3W1/3)O3–(x)BiFeO3 (x = 0.1 and 0.4) solid solution

We report on the structure, spin–lattice and magneto-electric coupling in (1−x)Pb(Fe2/3W1/3)O3–(x)BiFeO3(where x = 0.1 and 0.4) (PBFW) solid solution synthesized through two-step solid-state reaction method. The room temperature (RT) crystallographic studies were carried out using x-ray diffraction and neutron diffraction measurements which show a single-phase Pseudocubic crystal system with Pm-3m space group. Rietveld refinement was carried out to obtain the structural parameters using Fullprof software and the observed structural parameters are in good agreement with the previous reports. Temperature-dependent neutron diffraction measurements reveal the presence of commensurate G-type antiferromagnetic structure. The magnetic structure was analyzed using the propagation wave vector k ∼ (½ ½ ½) for both the solid solutions. The obtained lattice constants increase linearly and the magnetic moment decrease with temperature, which shows a remarkable anomaly around the magnetic (TN ∼ 405 K for x = 0.1 and 531 K for x = 0.4) transition temperatures. This anomaly clearly indicates the existence of spin–lattice and magnetoelectric coupling. The magnetic susceptibility (ZFC and FC at 500 Oe) and M–H hysteresis loop measurements show spontaneous magnetic moment due to the Fe3+–O2−–Fe3+ superexchange interaction coexisting with the weak ferromagnetism. Bifurcation of ZFC and FC curve reveals the strong anisotropic nature. Astonishingly, magnetic measurements show the non-zero magnetic moment above TN and broadening of the magnetic transition indicates the presence of short-range uncompensated sublattice weak ferromagnetic clusters in the paramagnetic region. The Mossbauer spectroscopy and electron paramagnetic resonance studies exhibit the RT magnetically ordered system and confirm the +3 state of Fe along with the fraction of Fe2+ ions.

Enhanced piezoelectric and electric field induced stain response in Bi0.5Na0.5TiO3–Ba(Zr0.055Ti0.945)O3 ceramics modified by (K0.5Na0.5)NbO3

Due to people pay more attention to environmental protection, lead-free piezoelectric ceramics have become the focus of contemporary research. In this paper, a new ternary (0.93−x)Bi0.5Na0.5TiO3–0.07Ba(Zr0.055Ti0.945)O3–x(K0.5Na0.5)NbO3 (BNT–BZT–xKNN) (x = 0, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07) solid solution were synthesized by two-step solid-state reaction method. The variations of ferroelectric, piezoelectric and electric field induced strain properties with composition were investigated. It is found that KNN substitution induces a ferroelectric to relaxor phase transition. The x = 0.01 sample dominated by ferroelectric phase shows improved d33 of 180 pC/N. The x = 0.02 sample with coexistence of the ergodic and nonergodic relaxor exhibits large unipolar strain of ~ 0.31% with low strain hysteresis of ~ 33.5% and the corresponding large signal d33* is ~ 476 pm/V. For the ceramics with x = 0.07, the ergodic relaxor is dominant, which shows the unipolar stain of ~ 0.27% under 90 kV/cm, accompanied by strain hysteresis of ~ 16.3%. From 30 to 150 °C, under the electric field of 60 kV/cm, the change of strain is ~ 25.8% and ~ 17.6% for 0.02 KNN and 0.07 KNN ceramics, respectively. Our results indicate BNT–BZT–xKNN ceramics with different KNN content are promising candidates for sensor and actuator applications.

Synthesis of novel Eu2+ activated K3Ca2(SO4)3F down-conversion phosphor for near UV excited white light emitting diode

In the present paper, we have successfully synthesized Eu2+ activated K3Ca2(SO4)3F phosphor by two-step solid-state reaction method at high temperature (800 °C). Pure crystalline formation, morphological behavior, and their vibration bonds of synthesized Eu2+ activated K3Ca2(SO4)3F phosphor were verified by the X-ray diffraction (XRD), Scanning Electron Microscopy (SEM) and Fourier transform Infrared Spectrum (FT-IR). The photoluminescence (PL) spectrum and CIE coordinate with color purity also characterized. In PL emission spectra clearly represented that broad excitation band from 250 nm to 400 nm ranged. The center of this PL excitation spectra observe at 326 nm, but some parts of these spectra lies to 350 nm–400 nm. This excitation wavelength is very useful for the generation of white light because it may be used as near UV light. PL emission represents broad emission spectra from 400 nm to 550 nm centred at 440 nm. Most part of these PL emission spectra lies in the blue region of the spectrum. PL spectra arise from the transitions between the 5d and 4f orbital’s transition of Eu2+ ions. EVI parameters such as Stokes Shift (ΔEs), the Huang-Rhys factor (S),effective phonon energy (ħω) and the Zero-phonon line (ZPL) are calculated. In our present work, we are calculated that the value of Huang–Rhys factor constant (S) is 3.74 that means coupling is intermediately strong. CIE chromaticity coordinate of K3Ca2(SO4)3F:xmol%Eu2+[x = 0.5, 2.0, 3.0, 5.0, 7.0, 10mol%] phosphor were also calculated by using OSRAM SYLVANIA color calculator 1931. By using these CIE chromaticity coordinate was calculated the value of color purity for each concentration of Eu2+ ions. After seeing all results of synthesized phosphor material we are concluded that it may be a better option used as commercial phosphor for obtaining white light. So it may be a promising candidate for NUV WLEDs.

An-harmonic Oscillations and Superconductivity in (Cu0.5-xKxTl0.5)Ba2Ca2Cu3-y-z ZnyCdzO10-δ (x = 0, 0.25; y = z = 0, 0.25, 0.5, 0.75, 1) Samples

(Cu0.5-xKxTl0.5)Ba2Ca2Cu3-y-z ZnyCdzO10-δ (x = 0, 0.25; y = z = 0, 0.25, 0.5, 0.75, 1) samples are synthesized for the investigation of role of an-harmonic oscillations in the mechanism of high Tc superconductivity. In the conducting planes, the carrier density is enhanced by K doping at the charge reservoir layer (Cu0.5Tl0.5)Ba2O4-δ by synthesizing (Cu0.25K0.25Tl0.5)Ba2Ca2Cu3-y-zZnyCdzO10-δ (y = z = 0, 0.25, 0.5, 0.75, 1) samples. The (Cu0.5-xKxTl0.5)Ba2Ca2Cu3-y-z ZnyCdzO10-δ (x = 0, 0.25; y = z = 0, 0.25, 0.5, 0.75, 1) samples were prepared by employing two-step solid-state reaction method accomplished at 860 °C and understand their superconducting properties by resistivity measurements, X-ray diffraction analysis, and FTIR absorption measurements. The orthorhombic unit cell of our samples was confirmed via XRD analysis. The analysis also reflected the increase in c-axis length and the volume of the unit cell with the enhanced dopants (Cd and Zn) concentration. The suppression of Tc(onset) and Tc(R = 0) was found with the increasing concentration of Zn and Cd. An improvement in the Tc(onset) observed in samples doped by K that arises due to increase in the density of free carriers supplied by alkali atoms. With the increasing content of Cd and Zn, the unit cell exhibits the softening of Cu(1)-OA-Cu(2) and Tl-OA-Cu(2) apical oxygen mode and hardening of planar oxygen mode. From FIC analysis, the Tcmf and T* and various cross over temperature were shifted towards lower temperature with the enhanced Zn and Cd dopant concentration. The value of α determining the defect density also increases with the increasing dopant (Zn and Cd) concentration. The numerical values of different parameter like Bc0(T), Bc1(T), Jc(0), and Ebreak showing increasing trend but the phase relaxation time of the carriers τφ points out decreasing trend with the enhanced doping of Cd and Zn. Moreover, these parameters reflected inferior values in K-doped samples relative to K-undoped samples. The value of other parameter like coherence length ξc(0) along c-axis, interlayer coupling J, magnetic field penetration depth λp.d, the Ginzburg Landau (GL) parameter κ, and the Fermi velocity VF of the carriers decreases as doping of Zn and Cd enhanced. These parameters show superior values in K-doped samples relative to K-undoped samples due to increase in the density of free carriers supplied by K atoms. The negative values of real part of dielectric constant suppress in both K undoped and K doped samples with increasing concentration of Cd and Zn. The imaginary part of dielectric constant and ac conductivity showing suppression in their negative values in K undoped samples while showing increase in absolute values in K doped samples with increasing concentration of Cd and Zn.

Optical and Structural Analysis of BaSi2O2N2:Eu Green Phosphor for High-Color-Rendering Lighting

Green BaSi2O2N2:0.02Eu2+ phosphor is synthesized through a two-step solid state reaction method. The first firing is for crystallization, and the second firing is for reduction of Eu3+ into Eu2+ and growth of crystal grains. By thermal analysis, the three-time endothermic reaction is confirmed: pyrolysis reaction of BaCO3 at 900 ºC and phase transitions at 1,300 ºC and 1,400 ºC. By structural analysis, it is confirmed that single phase [BaSi2O2N2] is obtained with Cmcm space group of orthorhombic structure. After the first firing the morphology is rod-like type and, after the second firing, the morphology becomes round. Our phosphor shows a green emission with a peak position of 495 nm and a peak width of 32 nm due to the 4f65d1→4f7 transition of Eu2+ ion. An LED package (chip size 5.6 x 3.0 mm) is fabricated with a mixture of our green BaSi2O2N2, and yellow Y3Al5O12 and red Sr2Si5N8 phosphors. The color rendering index (90) is higher than that of the mixture without our green phosphor (82), which indicates that this is an excellent green candidate for white LEDs with a deluxe color rendering index.

Investigation of space charge polarization behavior in Pb0.9Bi0.1Fe0.7W0.3O3 ceramic

The Pb0.9Bi0.1Fe0.7W0.3O3(PBFW) solid solution was successfully synthesized by the modified two-step solid state reaction method. Room temperature X-ray diffraction (XRD) confirms the Psuedocubic structure with Pm-3m space group and the lattice parameter a = 3.9756(6) Å. Frequency dependent dielectric permittivity and loss tangent were studied in the temperature range from 313 to 528 K. High dielectric permittivity at low-frequency region reveals the contribution of space charge polarization originated by the chemically 1:1 B site order in the system. Origin of SCP or Maxwell-Wagner polarization indicates the compositional heterogeneity in the ceramic. By observing the depressed semicircle in the cole –cole plot of impedance and well-fitting of Kohlraush-Williams-Watt function to the electric modulus reveals the PBFW follows the non-Debye type of relaxation mechanism and peak shifting reveals the transition of long range to short range mobility of charge carriers. The calculated activation energy from all the above studies confirms the presence of space charges in both grain and grain boundary; those are involved in the relaxation and conduction mechanism in all measured temperatures. Fitted Johnscher's power law for AC conductivity gives polaronic hopping conduction mechanism.

Synthesis, properties, and package of Eu2+ doped green-yellow Ba(Ca)SiO(N) phosphors in NUV LED

In the study, a two-step high temperature solid state reaction method was applied to synthesize the green and green-yellow phosphors of 0.5 mol% Eu2+ doped Ba2SiO4, mixture of Ba3Si6O9N4 and Ba2SiO4, CaSi2O2N2. X-ray diffraction (XRD), scanning electron microscope (SEM), diffuse reflection (DR) spectra, photoluminescence (PL) excitation and emission spectra, thermal stability behavior, and luminescent decay curves were employed to analyze these phosphors. In the first step reaction, Eu3+ present weak red or orange-red emission. After reduction from Eu3+ to Eu2+ in the N2(95%)–H2(5%) atmosphere in the second reaction step, the Eu2+ presented bright green or green-yellow light under near ultraviolet (NUV) excitation. By combining the phosphors with NUV chips, the obtained LEDs gave bright light under forward bias current. The obtained green and green yellow materials can be used in phosphor converted based LEDs.

Conductive mechanism and the enhancement high-power electrical properties of Mn-modified Bi(Sc3/4In1/4)O3–PbTiO3–Pb(Mg1/3Nb2/3)O3 high temperature piezoelectric ceramics

In this research, we report the improved high-power electrical properties and the conductive mechanism of the 0.40Bi(Sc3/4In1/4)O3–0.58PbTiO3–0.02Pb(Mg1/3Nb2/3)O3–xMnO2 (BSI–PT–PMN–xMn, x = 0.0–0.8) system synthesized by a modified two-step solid state reaction method. A pure perovskite phase has been detected by the X-ray diffraction analysis of the BSI–PT–PMN–xMn ceramics, and the mechanical quality factor Qm has been found to increase from 28 to 210 with Mn content increasing from 0.0 to 0.8. The DC resistivity measurement indicated that the resistivity of the BSI–PT–PMN–xMn ceramics increases firstly, reaching the maximum at x = 0.4, and then decreases with more Mn modified. The conduction behavior can be described by the intrinsic charge carriers conduction mechanism and extrinsic semiconductor conductive mechanism in different temperature range. The high DC resistivity over 109 Ω cm at 300 °C together with the good electrical properties of piezoelectric constant d33 336 pC/N, planar electromechanical coupling factor kp 42.8%, mechanical quality factor Qm 120 and Curie temperature Tc 414 °C of the BSI–PT–PMN–0.4Mn ceramics makes it promising candidates for high temperature high-power piezoelectric applications.