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The phosphors for pc-LEDs have high thermal stability requirements due to the high operating temperature of LEDs. In addition, there are many phosphors based on SrNb 2 O 6 , but no one has studied Sm3+ or Tb3+ as the luminescent center of SrNb 2 O 6 host. Therefore, two new phosphors based on SrNb 2 O 6 host are proposed in this work. One is an orange phosphor with negative thermal quenching phenomenon using Sm3+ as the luminescent center, and the other is a green phosphor with Tb3+ as the luminescent center. In this work, a series of SrNb 2 O 6 :Sm3+ and SrNb 2 O 6 :Tb3+ phosphors were prepared by the solid-state reaction method. The structure, morphology, chemical composition, absorption properties and luminescence properties of Sm3+ and Tb3+ doped SrNb 2 O 6 samples were studied. Under 405 nm excitation, the SrNb 2 O 6 :Sm3+ samples exhibit the 4f-4f transition of Sm3+ with the strongest emission intensity at 607 nm, the emission intensity of SrNb 2 O 6 :0.03Sm3+ phosphor at 150 °C remains at 100.56% of its room temperature value and the chromaticity coordinates are located in the orange region, with a color purity of 88.19%. Under 307 nm excitation, the SrNb 2 O 6 :Tb3+ samples exhibit the 4f-4f transition of Tb3+ with the strongest emission intensity at 544 nm, the emission intensity of SrNb 2 O 6 :0.09Tb3+ phosphor at 150 °C remains at 7.68% of its room temperature value and the chromaticity coordinates are located in the green region with a color purity of 74.29%. Additionally, Na+ is introduced as a charge compensator in the Sm3+ or Tb3+ doped phosphors, which enhances their luminescence intensity. These results indicate that the two phosphors synthesized in this work have the prospect of application in the field of solid-state lighting. [ABSTRACT FROM AUTHOR]

LiNbO3 is a commonly used cathode coating material in Li-ion batteries (LIBs). However, LiNbO3 has a poor ion transport capacity owing to the strong binding ability of the lattice structure to Li. In this study, a series of Li(1–x)Nb(1–x)WxO3 (x = 0–0.5) samples were synthesized by dissolving WO3 in LiNbO3, and the effects on structural changes and the ion transport capacity were studied. When x = 0.2, The lattice structure had not changed, but the activation energy was 0.5151 eV, and the ionic conductivity reached a maximum of 1.75 × 10− 6 S cm-1 at 90 ℃. When the amount of W was higher than the maximum solution amount, the LiNbWO6 tetragonal phase appeared, and the ionic conductivity decreased. This study provides a new method to improve the migration ability of Li ions in LiNbO3 and an experimental basis for subsequent studies on LiNbO3 with WO3 dissolving as a coating material for LIBs cathodes. [ABSTRACT FROM AUTHOR]

Potassium sodium niobates (KNNs) have garnered significant attention owing to their lead-free nature and potential for use in self-cleaning membranes. This paper presents the synthesis of (K 0.5 Na 0.5)NbO 3 materials for the fabrication of porous membranes, which enable in situ ultrasonic resonance to effectively eliminate contaminants from the membrane surface. KNN powder was synthesized via solid-state reactions, and the membranes were prepared using conventional sintering techniques. The effects of ball-milling time and calcination temperature on the phase structure, pore size, permeance, flexural strength, chemical stability, and piezoelectric properties were comprehensively investigated. The optimal membranes exhibited an average pore size of approximately 300 nm, a porosity of 23 %, and permeance of 220 L m−2 h−1 bar−1 at a sintering temperature of 1050 °C. A polarized electrical field with a strength of 1 kV/mm was applied to the membranes, resulting in an ultrasonic response of 20 mV at an excitation voltage of 20 V with a frequency of 200 kHz. Furthermore, the in situ anti-fouling performance was evaluated by conducting filtration tests on a 500 ppm oil-in-water (O/W) emulsion, demonstrating that the stationary flux increased by 46.7 % when subjected to an excitation voltage of 60 V. [ABSTRACT FROM AUTHOR]

High-entropy rare-earth niobates have garnered significant attention in the field of thermal barrier coatings (TBCs) due to their ultra-low thermal conductivity. However, the exceptional thermal properties of fluorite-phase high-entropy rare-earth niobates and the outstanding mechanical properties of monoclinic-phase high-entropy rare-earth niobates cannot be simultaneously harnessed. To address this limitation, this paper investigates and synthesizes five single-phase high-entropy rare-earth niobates: (RE 1/5 Ho 1/5 Er 1/5 Y 1/5 Yb 1/5) 3 NbO 7 (RE = Ce, Sm, Eu, Dy, Lu), and five composite-phase high-entropy rare-earth niobates with a molar ratio of (RE 1/5 Ho 1/5 Er 1/5 Y 1/5 Yb 1/5)NbO 7 : (RE 1/5 Ho 1/5 Er 1/5 Y 1/5 Yb 1/5)NbO 4 = 1:2 (RE = Ce, Sm, Eu, Dy, Lu). The objective is to fabricate niobate coatings that exhibit both outstanding thermal and mechanical properties. The test results reveal that the intrinsic thermal conductivity of the composite-phase samples stands at a mere 1.46 W m−1·K−1 at 1000 °C. Comparatively, the experimental thermal conductivity of the single-phase samples slightly surpasses that of the composite-phase at 1000 °C, registering a minimum of 1.57 W m−1·K−1. Importantly, both values adhere to the TBC standard. The mechanisms behind the low thermal conductivity of the composite-phase and single-phase samples are elucidated by the phonon scattering mechanism and the Cahill model, respectively. Furthermore, the thermal expansion coefficient of the composite-phase samples exceeds that of the single-phase samples overall, and they demonstrate exceptional mechanical properties, offering nearly twice the fracture toughness of the single-phase samples while maintaining high hardness. Experimental evidence shows that composite-phase niobates exhibit enhanced thermodynamic properties compared to single-phase niobates. This work serves as a valuable reference for the utilization of high-entropy rare-earth niobates in the realm of thermal barrier coatings. [ABSTRACT FROM AUTHOR]

A series of high entropy niobates with cation at A-site varying in size disorder and mass disorder is designed. High entropy niobates are all monoclinic structures with uniform rare-earth element distribution, but different space groups, which are closely related to the average radius at A-site. High entropy niobates possess excellent sintering resistance and ultra-low thermal conductivity due to stronger phonon-point defect scattering and shorter phonon lifetime. The effect of high entropy on average grain size and thermal conductivity is inversely proportional to size disorder. Moreover, the radiative heat transfer of (Dy 0.2 Ho 0.2 Er 0.2 Y 0.2 Yb 0.2)NbO 4 is substantially reduced due to the co-doping of active multi-component Dy3+, Er3+, and Yb3+, which broadens the range of intrinsic absorption band and improves lattice absorption derived from lattice distortion. Besides, the (La 0.2 Nd 0.2 Sm 0.2 Eu 0.2 Y 0.2)NbO 4 exhibits an ultra-high thermal expansion coefficient (12.34 ×10−6 K−1, 673 °C). The excellent thermophysical properties imply that high entropy niobates are more promising thermal barrier coating materials. [ABSTRACT FROM AUTHOR]

This study investigates the fracture toughness and toughening mechanism of (La0.2Nd0.2Sm0.2Eu0.2Y0.2)NbO4, a high entropy material characterized by a high thermal expansion coefficient and low thermal conductivity. Our finding demonstrates a noteworthy 50% increase in fracture toughness for (La0.2Nd0.2Sm0.2Eu0.2Y0.2)NbO4 (~3.09 MPa m0.5) compared to YNbO4 (~2.11 MPa m0.5). The superior fracture toughness for (La0.2Nd0.2Sm0.2Eu0.2Y0.2)NbO4 can be attributed to the two key factors: relatively easy ferroelastic domain switching and the presence of ultrahigh-density dislocations (~7 x 108 mm-2). The enhanced ferroelastic toughening in (La0.2Nd0.2Sm0.2Eu0.2Y0.2)NbO4 is associated with its distinct characteristics, large atomic radius (RA), significant tetragonality (c/a ratio), and lowmonoclinic β angle. These factors contribute to larger spontaneous strain, larger coercive strain, and lower transformation strain, respectively. These properties facilitate the formation and switching of the ferroelastic domains. In addition, the interactions between the large strain field surrounding the dislocations and the cracks facilitate crack deflection and bridging. The combined effect of ferroelastic toughening and ultrahigh-density dislocations ultimately leads to the significant improvement in the fracture toughness of (La0.2Nd0.2Sm0.2Eu0.2Y0.2)NbO4. [ABSTRACT FROM AUTHOR]

The pseudo-ilmenite structure ABO3 have been increasingly highlighted in the optoelectronic area. Nanoparticles of undoped lithium niobates (LiNbO3) and codoped with rare earths (LiNbO3: Dy3+/Tb3+) were synthesized by the solid-state reaction method and calcined in a controlled way. The properties and structural changes of niobates were evaluated from data obtained in XRD and Rietveld refinement. The SEM-FEG micrographs showed different morphologies obtained (cubes, plates, tetrahedrons and polyhedra) according to the variation of the doping and co-doping process. Optical properties were measured and studied based on the results obtained from the UV-Vis spectrophotometer and photoluminescence assays. The photoluminescence presented by LiNbO3 was associated with the existence of superficial defects in the particles, i.e., centers of recombination of photogenerated charges favorable to the property. The effect of concentration of dopants was investigated in properties photoluminescence. Photometric measurements (CRI, purity, CCT, LER) were analyzed and a modulation of the emitted color as a function of the concentration of the dopants. According to the obtained results, LiNbO3: Dy3+/Tb3+ presents itself as a material with great potential in optical device applications. [ABSTRACT FROM AUTHOR]

The pseudo-ilmenite structure ABO3 have been increasingly highlighted in the optoelectronic area. Nanoparticles of undoped lithium niobates (LiNbO3) and codoped with rare earths (LiNbO3: Dy3+/Tb3+) were synthesized by the solid-state reaction method and calcined in a controlled way. The properties and structural changes of niobates were evaluated from data obtained in XRD and Rietveld refinement. The SEM-FEG micrographs showed different morphologies obtained (cubes, plates, tetrahedrons and polyhedra) according to the variation of the doping and co-doping process. Optical properties were measured and studied based on the results obtained from the UV-Vis spectrophotometer and photoluminescence assays. The photoluminescence presented by LiNbO3 was associated with the existence of superficial defects in the particles, i.e., centers of recombination of photogenerated charges favorable to the property. The effect of concentration of dopants was investigated in properties photoluminescence. Photometric measurements (CRI, purity, CCT, LER) were analyzed and a modulation of the emitted color as a function of the concentration of the dopants. According to the obtained results, LiNbO3: Dy3+/Tb3+ presents itself as a material with great potential in optical device applications. [ABSTRACT FROM AUTHOR]

Herein, we demonstrate the photoluminescence properties of Dy3+-activated YNbO4, LuNbO4, and mixed YxLu1−xNbO4:Dy3+ (x = 0.25, 0.5, 0.75) phosphors. For this purpose, five samples with a fixed Dy3+ concentration (2 mol%) were prepared by the solid-state reaction method. X-ray diffraction measurements showed that all phosphors crystallize in a monoclinic fergusonite-beta-(Y) structure with a C2/c space group. Scanning electron microscopy clearly shows that samples are composed of dense, well-developed micron-sized, cube-shaped grains with rounded edges. The photoluminescent emission spectra feature Dy3+ peaks at standard positions corresponding to transitions from the 4F9/2 excited emitting level to the 6HJ (J = 15/2; 13/2; 11/2 and 9/2) lower levels with two dominant emission bands placed in the blue (~ 479 nm, B) and yellow (~ 576 nm, Y) spectral region. It is observed that with Lu increase in the host lattice Y/B ratio decreases toward the desired ratio of unity to obtain white light. To evaluate the suitability of these phosphors for use in solid-state lighting, their photoluminescence emission was analyzed in detail by calculating CIE coordinates, correlated color temperature (CCT) and Delta u,v (DUV). It is shown that CIE chromaticity coordinates of all Dy3+-activated YxLu1−xNbO4 samples (x = 0, 0.25, 0.5, 0.75, and 1) fall into the white portion of the diagram and that with the increase of Lu in the host lattice color becomes whiter. CCT values for all samples are in the cooler 4000–4500 K range with positive DUVs indicating that color points are placed above the black body curve. The average lifetime of 4F9/2 level is calculated to be ~ 0.2 ms for all Dy3+-activated YxLu1−xNbO4 samples, indicating that there is no influence of the Y-to-Lu ratio in the host niobate material on the luminescence kinetics. [ABSTRACT FROM AUTHOR]

A new ultraviolet photodetector (UV PD) is successfully fabricated based on 2D NbWO6 (NWO) nanosheets for the first time, which is synthesized by a facile solid‐state reaction, ion exchange and liquid exfoliation process. The NWO nanosheet‐based PDs exhibit excellent UV detecting performance at 1 V at 290 nm, high responsivity (378 A W−1), high external quantum efficiency (EQE, 1.6 × 104%), high spectral selectivity (R290/R400 = 8.84 × 103) and fast speed (1.05/88 ms). Furthermore, the NbWO6 nanosheets film based PD shows great potential for the application in UV image sensing. This work provides a feasible strategy for the development of new UV PDs based on other potential layered niobates. [ABSTRACT FROM AUTHOR]

Single‐phase barium sodium niobate phosphor (Ba2NaNb5O15: BNNO) doped with europium (Eu3+) ions have been synthesized by solid‐state reaction route. Pure and single‐phase formation with the tetragonal structure of the synthesized Eu3+‐doped BNNO (BNNO: Eu3+) phosphor was confirmed by X‐ray diffraction. The SEM image of BNNO sample indicates irregular morphology and nonuniform micron‐sized particle formation. The intense excitation peak located at 463 nm appeared in the excitation spectrum for BNNO: Eu3+ phosphors when monitored atred (615 nm) emission of Eu3+ ions. Under 463 nm excitation, the emission spectra for BNNO: Eu3+ exhibit dominant red (615 nm) emission peak. The luminescence intensity increases progressively up to the 10.0 mol% of Eu3+ ions and decreases further due to the concertation quenching effect. The energy transfer mechanism responsible for concentration quenching has been investigated in detail. The chromaticity coordinates assessed for BNNO: Eu3+ phosphors, which are located in the red region of Commission International de l'Eclairage 1931 diagram. The structural, morphological, and spectroscopic results attained for the synthesized phosphor (BNNO: Eu3+) demonstrate potential candidature as a red component phosphor in solid‐state lighting applications. [ABSTRACT FROM AUTHOR]

We have used a recently introduced new tolerance factor τ to create a stability map of all possible A-site double perovskite titanates AA′Ti2O6 and niobates AA′Nb2O6. The predictive power of τ is relatively good based on comparisons with available experimental data for A-site double perovskites. We carried out quantum chemical calculations on two hypothetical double perovskite compositions CsScTi2O6 and YRbTi2O6, where τ predicts high probability for their existence. In both cases, we found limits in the predictive power of the new tolerance factor for ion combinations on the A and A′ site which are very different in size. A difference in oxidation state may decrease the accuracy, as well. Overall, the A-site double perovskite stability mapping provides a starting point for the discovery of novel A-site double perovskites. [ABSTRACT FROM AUTHOR]

Series of ceramics based on Gd 1-x Eu x Nb y Ta 1-y O 4 (x = 0.01; 0.02; 0.06; 0.1; 0.2; 0.4) solid solutions with different Nb\Ta ratio were obtained for the first time. A detailed study of the structural and cathodoluminescent (CL) properties of the obtained materials was carried out. All samples had a monoclinic structure with I2/a space group (M-polytype). The content of phase impurities in some samples did not exceed 3-10 rel.%. CL bands attributed to transitions from 5D 0 , 5D 1 , 5D 2 , 5D 3 levels to the 7F j (j = 0-5) Eu3+ levels were observed in the CL spectra in the range of 350-750 nm. Concentration quenching of Eu3+ ions CL intensity occurred at concentrations from 0.1 to 0.2 form. un. of Eu3+. The Eu3+ CL intensity did not evidently depend on the Nb/Ta ratio for most of the samples. 5D 0 -7F 2 Eu3+ transition decay kinetics was approximated with the sum of two exponentials. The presence of shorter decay time was associated with Eu3+ luminescence centers with an increased probability of nonradiative recombination located near extended defects and ceramic grain boundaries. [ABSTRACT FROM AUTHOR]

Phase transformations in the lithium aluminosilicate glass nucleated by a mixture of yttrium and niobium oxides and doped with cobalt ions were studied for the development of multifunctional transparent glass-ceramics. Initial glass and glass-ceramics obtained by isothermal heat-treatments at 700–900 °C contain YNbO4 nanocrystals with the distorted tetragonal structure. In samples heated at 1000 °C and above, the monoclinic features are observed. High-temperature X-ray diffraction technique clarifies the mechanism of the monoclinic yttrium orthoniobate formation, which occurs not upon high-temperature heat-treatments above 900 °C but at cooling the glass-ceramics after such heat-treatments, when YNbO4 nanocrystals with tetragonal structure undergo the second-order transformation at ~550 °C. Lithium aluminosilicate solid solutions (ss) with β-quartz structure are the main crystalline phase of glass-ceramics prepared in the temperature range of 800–1000 °C. These structural transformations are confirmed by Raman spectroscopy and illustrated by SEM study. The absorption spectrum of the material changes only with crystallization of the β-quartz ss due to entering the Co2+ ions into this phase mainly in octahedral coordination, substituting for Li+ ions. At the crystallization temperature of 1000 °C, the Co2+ coordination in the β-quartz solid solutions changes to tetrahedral one. Transparent glass-ceramics have a thermal expansion coefficient of about 10 × 10−7 K−1. [ABSTRACT FROM AUTHOR]

Phase relationships of the Nb2O5-MgO-SiO2 system in equilibrium at 1673 K and 1523 K in air have been investigated by the high-temperature equilibration/quenching method. The compositions of equilibrium phase were determined by electron-probe X-ray microanalysis (EPMA) and X-ray diffraction (XRD). In this study, no ternary compounds were observed. The isothermal section of the system at 1673 K was triangulated into seven three-phase regions: SiO2-Nb2O5-Mg2/3Nb34/3O29, SiO2-Mg2/3Nb34/3O29-MgNb2O6, SiO2-MgSiO3-MgNb2O6, MgO-Mg2SiO4-Mg4Nb2O9, Mg2SiO4-MgNb2O6-Mg5Nb4O15, MgSiO3-Mg2SiO4-MgNb2O6, and Mg2SiO4-Mg5Nb4O15-Mg4Nb2O9. Similarly, the isothermal section at 1523 K was triangulated into six three-phase regions: SiO2-Nb2O5-MgNb2O6 region, SiO2-MgSiO3-MgNb2O6 region, MgO-Mg2SiO4-Mg4Nb2O9 region, Mg2SiO4-MgNb2O6-Mg5Nb4O15 region, MgSiO3-Mg2SiO4-MgNb2O6 region, and Mg2SiO4-Mg5Nb4O15-Mg4Nb2O9 region. The determination of the Nb2O5-MgO-SiO2 ternary system further enriches the thermodynamic databases of silicates and niobates. [ABSTRACT FROM AUTHOR]

Niobate Li+‐storage anode materials with shear ReO3 crystal structures have attracted intensive attention due to their inherent safety and large capacities. However, they generally suffer from limited rate performance, cyclic stability, and temperature adaptability, which are rooted in their insufficient interlayer spacings. Here, sodium niobate (NaNb13O33) micron‐sized particles are developed as a new anode material owning the largest interlayer spacing among the known shear ReO3‐type niobates. The large interlayer spacing of NaNb13O33 enables very fast Li+ diffusivity, remarkably contributing to its superior rate performance with a 2500 to 125 mA g−1 capacity percentage of 63.2%. Moreover, its large interlayer spacing increases the volume‐accommodation capability during lithiation, allowing small unit‐cell‐volume variations (maximum 6.02%), which leads to its outstanding cyclic stability with 87.9% capacity retention after as long as 5000 cycles at 2500 mA g−1. Its cyclic stability is the best in the research field of niobate micron‐sized particles, and comparable to that of "zero‐strain" Li4Ti5O12. At a low temperature of −10 °C, it also exhibits high rate performance with a 1250 to 125 mA g−1 capacity percentage of 65.6%, and even better cyclic stability with 105.4% capacity retention after 5000 cycles at 1250 mA g−1. These comprehensively good electrochemical results pave the way for the practical application of NaNb13O33 in high‐performance Li+ storage. [ABSTRACT FROM AUTHOR]

The article presents a study on the grain morphology of KNNLiLaTa0.1 piezoceramics obtained from the NaNbO3 precursor. It is mentioned that alternatives to lead zirconate titanate (PZT) compound are being sought due to high lead contents. The study focuses on the NaNbO3 precursor and establishes the correlation between its microstructural properties and the properties of KNNLiLaTa0.1. X-ray diffraction analysis and scanning electron microscopy were performed to study the morphology of the NaNbO3 and KNNLiLaTa0.1 systems. It was found that the KNNLiLaTa0.1 system presents a bimodal distribution of grain sizes due to the presence of dopants such as La. [Extracted from the article]

Tailoring the structure and properties of materials using the high‐entropy (HE) effect is of significant interest in the fields of environmental and thermal barrier coatings (TBCs). In this work, a new class of dense HE rare‐earth niobates was successfully prepared by a solid‐phase reaction method, including (Sm1/5Dy1/5Ho1/5Er1/5Yb1/5)NbO4 (5HERN), (Sm1/6Dy1/6Ho1/6Er1/6Yb1/6Lu1/6)NbO4 (6HERN), (Sm1/7Dy1/7Ho1/7Er1/7Yb1/7Lu1/7Gd1/7)NbO4 (7HERN), and (Sm1/8Dy1/8Ho1/8Er1/8Yb1/8Lu1/8Gd1/8Tm1/8)NbO4 (8HERN), along with eight single rare‐earth niobates (RENbO4, RE = Sm, Dy, Ho, Er, Yb, Lu, Gd, and Tm). X‐ray diffraction analysis showed that 5–8HERN are single‐phase solid solutions with a monoclinic structure (space group C12/c1). The thermal expansion coefficients of 7HERN and 8HERN exceed 11 × 10−6 K−1 at 1200°C and are much higher than those of the RENbO4 compositions (10.13–10.74 × 10−6 K−1) and other some HE rare‐earth oxides (10.27–10.87 × 10−6 K−1). Importantly, 5–8HERN have lower oxygen‐ion conductivity and higher activation energy than yttrium‐stabilized zirconia (YSZ) and the RENbO4 compositions. The oxygen‐ion conductivity of 5HERN (7.52 × 10−7 S cm−1, 900°C) was 105 times lower than that of YSZ (0.01 S cm−1, 750°C). The hardness of 5–8HERN is ∼7.81–8.46 GPa and these compositions have low intrinsic lattice thermal conductivity at high temperature (1.28–1.69 W m−1 K−1 at 900°C). The mechanism by which the HE effect improved the material properties was elucidated. Young's modulus, hardness, thermal expansion coefficient, and intrinsic lattice thermal conductivity are linearly related to the mass, size, and distortion degree of samples. In contrast, the oxygen‐ion conductivity depends on both the degrees of disorder and distortion and the oxygen‐ion vacancy concentration. Based on their overall performance, especially their high thermal expansion coefficients and excellent oxygen‐barrier performance, HE rare‐earth niobates show potential for further development as TBC materials. [ABSTRACT FROM AUTHOR]

The impact of the crystallinity on structural, thermal, and in vitro dissolution properties were examined for Na 2 O-CaO-Nb 2 O 5 /MgO-P 2 O 5 glasses/glass-ceramics. Glass-ceramics were synthesized via a spontaneous crystallization process. The Nb content in the materials increased with melting temperature, furthermore, the crystallinity is proportional to the Nb content. The presence of crystalline niobates and phosphates is confirmed by FTIR analysis which is consistent with XRD. The FTIR results indicate that the phosphate network is built of different proportions of Q2, Q1, and Q0 units, depending on the amount and type of crystalline phase. Most of the samples show an improvement in thermal stability. The in vitro dissolution test showed that the highest mass loss for most of the samples occurred during the first 6 days of immersion in the PBS solution. The presence of small phosphate crystals favors the deposition of hydroxyapatite on samples' surfaces while the larger niobate crystals dissolve more readily. [ABSTRACT FROM AUTHOR]

In this paper, a series of high-entropy rare earth niobates, including fluorite RE 3 NbO 7 (HE317), monoclinic RENbO 4 (HE114) and RENbO 4 /RE 3 NbO 7 composite (HE-composite), are prepared via solid state reaction, following by a study about their thermal and mechanical properties. The high-entropy rare earth niobates exhibit excellent phase stability after thermally exposed to 1300 °C for 100 h, indicating entropy can stabilized high-entropy rare earth niobates. Compared with the single element rare earth niobates, high-entropy rare earth niobates have higher fracture toughness and hardness. The high-entropy RENbO 4 /RE 3 NbO 7 composite has the best mechanical properties, with a fracture toughness of 2.71 ± 0.17 MPa·m1/2 and hardness of 9.46 ± 0.24 GPa, respectively. The high-entropy niobates exhibit high coefficients of thermal expansion which is close to 7 wt% Y 2 O 3 stabilized ZrO 2. It is also proved that the configurational entropy has little effect on the critical temperature from monoclinic to tetragonal phase transition. The thermal conductivity of HE-composite is lower than HE114, indicating the combination of HE114 and H317 is a more efficient strategy to decrease the thermal conductivity of HE114 than entropy engineering. [ABSTRACT FROM AUTHOR]

The SrO-Nb2O5 system, especially Sr5Nb4O15 compound is of interest for their use as an electroceramics. In this work, Sr5Nb4O15 compound was synthesized by solid-state reaction and characterised by XRD. Thermodynamic properties like heat capacity, enthalpy of formation and Gibbs energy of formation of Sr5Nb4O15 have been measured. The standard molar enthalpy of formation of Sr5Nb4O15(s) was determined using an oxide melt solution high temperature calorimeter. Based on these experimental data, a self-consistent thermodynamic function of this compound was also generated. This thermodynamic data is essential for the optimization of synthesis conditions for materials and for the evaluation of their stability under appropriate technological operating conditions. [ABSTRACT FROM AUTHOR]

Nanoparticles of LiNbO3 and NaNbO3 were obtained for the first time by microwave-assisted combustion. Preliminary experiments reveal that the synthetic conditions influence their microstructure and optoelectronic features. Therefore, there is a need for performing the structural characterization of these materials, obtained by this new route. In the case of NaNbO3, there are two polimorphs which are stable at room temperature, space groups P21ma and Pbma. Powder x-Ray diffraction experiments were not capable to identify the crystalline phases present in the nanoparticles. Therefore, we have performed a detailed structural characterization of the nanoparticles by 1D and 2D solid state 23Na and 93Nb Nuclear Magnetic Resonance (NMR) techniques. 23Na results reveal the presence of both phases, Pbma and P21ma, for samples prepared using NaNO3 precursor in a 1:1 Na:Nb ratio or NaCl in excess. On the other hand, the P21ma polymorph could be isolated in the synthesis using NaCl salt in 1:1 Na:Nb ratio. On the other hand, LiNbO3 nanoparticles display the usual rhombohedral structure R3c. 7Li MAS NMR results reveal the presence of two types of Li species, with distinct dynamics. Highly mobile Li+ ions are found at the surface of the nanoparticles, while bulk Li+ show restricted movement. Finally, as a proof of principle, the photocatalytic activity of these niobates was tested for the degradation of methylene blue dye, a common organic-water contaminant.

To study a ferroelectric–graphene heterostructure, we employ Ginzburg–Landau–Devonshire theory in conjunction with Kretschmer and Binder's extrapolation-length method for modeling interface lattice relaxation. We rigorously justify a selection of model parameters that we use to predict the properties of a system consisting of the ferroelectric lithium niobate (LiNbO3) (0001) sandwiched between graphene monolayers. By comparing our results to those from first-principles density-functional theory calculations performed by Baeumer et al. [Nat. Commun. 6, 6136 (2015)] for the equivalent system, we demonstrate the inadequacy of the extrapolation-length method for modeling this system. We discuss the relevance of our work to predicting electrical gating. [ABSTRACT FROM AUTHOR]

We have evaluated the structural and luminescence properties of Eu3+- or Nd3+-doped lanthanum niobate systems synthesized via a sol–gel route and containing different dopant contents. XRD analysis revealed that the orthorhombic La3NbO7 and monoclinic LaNbO4 crystalline phases were present in all the samples, regardless of the dopant concentration. The excitation spectra of the samples displayed a broad band due to Nb5+→O2− charge transfer; this band was quite sensitive to the increasing Eu3+ content. The photoluminescence emission spectra of the samples with a lower Eu3+ content showed that Eu3+ occupied both crystalline phases. However, when the Eu3+ content increased, these ions preferentially occupied the C2 symmetry sites in the LaNbO4 host lattice. There was no emission quenching for the Eu3+-doped samples with a Eu3+ content as high as 20 mol%. The emission spectra of the Nd3+-doped samples displayed an intense emission band in the NIR-II biological window under NIR-I excitation, at 808 nm. In the case of the samples with a lower Nd3+ content, Nd3+ occupied distinct symmetry sites in La3NbO7. In contrast, in the samples with a higher Nd3+ content, these ions preferentially occupied LaNbO4 sites. The Nd3+ concentration that quenched emission in the Nd3+-doped samples was about 2.6 mol%, due to Nd3+–Nd3+ cross-relaxation processes. On the basis of these findings, the Eu3+-doped samples explored herein have promising applications in the lighting field, whereas the Nd3+-doped samples have potential use as solid-state lasers and biomarkers. [ABSTRACT FROM AUTHOR]

Phenol and its derivatives are present in effluents from several industrial processes, such as petroleum refining (produced water) and the pharmaceutical industry, and they are highly toxic. The present work elaborated a new catalyst for the removal of phenol and its derivatives. The photocatalyst was prepared by a simple method from the ammonium oxalate of niobium and nickel nitrate, resulting in heterostructures (principally NaNbO3/NaNb3O8 and a lesser amount of NiO) named NiNb. Platinum was deposited on this catalyst (NiNb/Pt catalyst), and its photocatalytic activity was tested on the degradation of phenol in seawater and distilled water, in the presence and absence of UV-C light (germicidal, λ = 254 nm), and with varying concentrations of platinum and varying pH of the solution. The catalyst was characterized by different techniques (SEM, EDS, DRS, XRD, TXRF, SBET,). The results of the study showed that the NiNb/Pt catalyst achieved 65% phenol removal in seawater and about 57% removal in distilled water. The reuse of the catalyst was also studied, and the photocatalytic mechanism was investigated by tests with scavenger agents and terephthalic acid. [ABSTRACT FROM AUTHOR]

A traditional solid-phase sintering technique was used to prepare the (0.98-x)K0.4Na0.6Nb0.94Sb0.04O3-xBi0.5Li0.5ZrO3-0.02SrZrO3 ternary ceramics, whose crystal structures were identified by X-ray diffraction method combined with dielectric-temperature measurements. It was found that there existed a rhombohedral-orthorhombic-tetragonal phase boundary when x = 0.03 to 0.04. The maximum values of piezoelectric constant d33 and planar electromechanical coupling coefficients kp both appeared at x = 0.03, being 263 pC/N and 0.39, respectively. Furthermore, adding too much Bi0.5Li0.5ZrO3 was noted to hinder the grain growth of the ceramics via the observation of microstructures with a scanning electron microscope. [ABSTRACT FROM AUTHOR]

This paper presents the application of an ordinary sintering process for 3 h in air to fabricate highly dense (Na0.52K0.44Li0.04)(Nb0.88Sb0.08Ta0.04)O3 (NKN-LST) ceramics with excellent piezoelectric properties at a lower sintering temperature through the use of excess Na2O as a sintering aid. The effects of sintering temperature in the range 940–1100 °C and Na2O addition in the range of 0 to 3.0 mol% on the density, sintering behavior, microstructure, dielectric and piezoelectric properties of the NKN-LST ceramics are investigated. Analysis reveals that NKN-LST ceramics samples sintered at 1020 °C for 3 h in air with 1.5 mol% excess Na2O achieve the highest electromechanical coupling factor and piezoelectric coefficient values of 0.45 and 364 pC/N, respectively. [ABSTRACT FROM AUTHOR]

Y 3 NbO 7 :xEu3+ powders (x = 0.25, 0.5, 0.75, 2, 3, 5, 10 at%) were synthesized by a two-step vibrational milling, alternating with annealing. All the samples crystallize as fluorite-type structure (space group F m 3 ‾ m ), with crystallite size 50–60 nm and show a strong orange/red luminescence with an excited state lifetime around 1.2 ms. Photoluminescence excitation and emission spectra show rapid intensity decline after 3 at% of Eu3+ content, indicating this concentration as critical for the concentration quenching, and we predicted multipolar interaction as the dominant mechanism behind it. Judd–Ofelt intensity parameters (Ω 2 = 0.941∙10−20 cm2, Ω 4 = 0.277∙10−20 cm2, Ω 6 = 0.277∙10−20 cm2) were obtained from the excitation spectrum of Y 3 NbO 7 :3 at%Eu3+. The emission of this luminescent powder is characterized by radiative and nonradiative lifetimes of 2.3 ms and 2.4 ms, respectively, and an intrinsic quantum yield of 51.5%. [Display omitted] [ABSTRACT FROM AUTHOR]

Ferroelectric lead-free NaNbO 3 -based ceramics are the most promising candidates to a wide range of advanced technological applications as sensors, transducers and actuators. In special, (K,Na)NbO 3 (KNN) and (Ba,Na)(Ti,Nb)O 3 (BTNN) show interesting structural properties, including morphotropic phase boundaries regions that lead to exceptional dielectric, piezoelectric and ferroelectric responses. Also, the biocompatibility of these compounds allows their application as biomedical sensors, medical devices, and bone tissue replacement. In this way, high impact applications can be achieved with ferroelectric lead free NaNbO 3 – based (NN-based) ceramics. In this review, we will explore the strategies for the improvement of ferroelectric, dielectric and structural properties reviewing the effects of the synthesis process, microstructure and chemical composition of lead-free complex perovskite ceramics, specially KNN and BTNN, as well as, PVDF-KNN and PVDF-BTNN polymer-ceramic and the (PVDF-TrFE)-KNN copolymer-ceramic composites to provide new insights and research opportunities for the development and improvement of fundamental properties of such systems considering their potential for technological applications, especially for the biological ones. [ABSTRACT FROM AUTHOR]

Optimization of mechanical properties in La 2 Zr 2 O 7 (LZO) ceramics, composites and coatings is an on-going requirement for their practical application. Herein, the contribution of monoclinic (La, Gd)NbO 4 (m-LGNO) enhancement of fracture toughness by ∼56% reveals its capability to be a prominent toughening agent. Due to the ferroelastic nature of LGNO, ferroelastic switching takes place within the stress concentrated regions, giving rise to significant strain energy relaxation. Atomic-scale evidence reveals that ferroelastic 94°/86° domain switching can occur, yielding merged 94° domains and newly formed 86° domains. The relevant strains induced by ferroelastic domain switching are quantified up to 8.06% and 6.20% in shear and normal strain, respectively. Such domain switching strains highlight their contribution to accommodate external mechanical loading for the 50 mol% GNO-LZO composite. The results indicate that the unique ferroelastic nature and 94°/86° ferroelastic domain switching in m-LGNO cooperatively provide a significant toughening effect. [Display omitted] [ABSTRACT FROM AUTHOR]

In most beam steering applications such as 3D printing and in vivo imaging, one of the essential challenges has been high-resolution high-speed multi-dimensional optical beam scanning. Although the pre-injected space charge controlled potassium tantalate niobate (KTN) deflectors can achieve speeds in the nanosecond regime, they deflect in only one dimension. In order to develop a high-resolution high-speed multi-dimensional KTN deflector, we studied the deflection behavior of KTN deflectors in the case of coexisting pre-injected space charge and composition gradient. We find that such coexistence can enable new functionalities of KTN crystal based electro-optic deflectors. When the direction of the composition gradient is parallel to the direction of the external electric field, the zero-deflection position can be shifted, which can reduce the internal electric field induced beam distortion, and thus enhance the resolution. When the direction of the composition gradient is perpendicular to the direction of the external electric field, two-dimensional beam scanning can be achieved by harnessing only one single piece of KTN crystal, which can result in a compact, high-speed two-dimensional deflector. Both theoretical analyses and experiments are conducted, which are consistent with each other. These new functionalities can expedite the usage of KTN deflection in many applications such as high-speed 3D printing, high-speed, high-resolution imaging, and free space broadband optical communication. [ABSTRACT FROM AUTHOR]

The paper presents the results of studying the polarization properties of solid solutions ceramics, including sodium and calcium niobates at room temperature and frequency f = 50 Hz. Three classification regions of the dielectric hysteresis loops formation were identified. The nature of observed effects formations was determined. [ABSTRACT FROM AUTHOR]

In this work. we studied the photocurrent behavior in (1-x)(K0.5Na0.5) (Nb0.93Sb0.07)O3–xBaTiO3+0.5 mol.%MnO2, (KNNS7–xBT) ceramics illuminated by light in the optical range of 0.15 mW/cm2. We detected a decrease in values of both maximum current and steady-state current in the area of structural phase transition temperature. The influence of long-term sample (aging) exposure on the behavior of maximum current (Imax) and steady-state current (Ist) values was revealed. After a certain period of time, the Imax values remained constant for the entire time interval, in contrast to the Ist values, which always decreased over time. [ABSTRACT FROM AUTHOR]

The photocatalytic properties of layered semiconductors, namely KNb3O8, and a product of its acid treatment, namely K3H3Nb10.8O30 in the reduction reaction of silver ions with the formation of the corresponding metal-semiconductor nanostructures are established. Electron microscopy has shown that silver nanoparticles are deposited mainly on the edges of niobate rods and plates when potassium niobate suspensions are irradiated with UV light in the presence of AgNO3. Silver nanoparticles of 10-30 nm are formed when K3H3Nb10.8O30 is used as a photocatalyst; they are deposited on the niobate surface and practically do not have a surface plasmon resonance band in the visible range of the spectrum, which may be associated with the formation of Ag2O on the surface of silver nanoparticles or the formation of their chain aggregates. [ABSTRACT FROM AUTHOR]

Eu3+-doped YxLu1−xNbO4 (x = 0, 0.25, 0.5, 0.75, 1) were prepared by the solid-state reaction method. YNbO4:Eu3+ and LuNbO4:Eu3+ crystallize as beta-Fergusonite (SG no. 15) in 1–10 μm diameter particles. Photoluminescence emission spectra show a slight linear variation of emission energies and intensities with the solid-solution composition in terms of Y/Lu content. The energy difference between Stark sublevels of 5D0→7F1 emission increases, while the asymmetry ratio decreases with the composition. From the dispersion relations of pure YNbO4 and LuNbO4, the refractive index values for each concentration and emission wavelength are estimated. The Ω2 Judd–Ofelt parameter shows a linear increase from 6.75 to 7.48 × 10−20 cm2 from x = 0 to 1, respectively, and Ω4 from 2.69 to 2.95 × 10−20 cm2. The lowest non-radiative deexcitation rate was observed with x = 1, and thus LuNbO4:Eu3+ is more efficient phosphor than YNbO4:Eu3+. [ABSTRACT FROM AUTHOR]

The remote and non-invasive optical thermometer exploiting fluorescence intensity ratio technology is of great importance in various intelligent optoelectronic sensors. Dual-emitting YNbO 4 :Bi3+, Eu3+ phosphor is synthesized and investigated for the development of temperature sensing materials. The phosphor excited at 318 nm shows a blue broad band emission and several red sharp peaks. The value of Bi3+→Eu3+ energy transfer can reach 98.2% when Eu3+ doping content is 0.14. Benefiting from diverse thermal response behaviors due to Bi3+ and Eu3+ ions completely different electronic configurations, a dual-emitting optical thermometer is designed. The maximum values of absolute and relative sensitivities are as high as 2.51% K−1 at 473 K and 1.43% K−1 at 423 K, respectively. The thermochromic phosphor possesses a great chromaticity shift (ΔE = 317×10−3) with temperature. Based on superior color discriminability, visual colorimetry temperature measurement relied on thermal characteristic is proposed. All the results demonstrate that YNbO 4 :0.01Bi3+, 0.005Eu3+ phosphor as a sensitive and reliable optical thermometer has great potentials in temperature measurement. [ABSTRACT FROM AUTHOR]

MnO2 added potassium sodium niobate (KNN) electroceramics were prepared by conventional double sintering ceramic route. The samples prepared have the compositional formula K0.5Na0.5NbO3+ (x)MnO2 where x = 0 wt%, 5 wt%, 10 wt%, 15 wt%, 20 wt% and 25 wt% is the amount of MnO2 added. The sintering of the samples was done using the microwave sintering technique. Pre-sintering was done at 850 °C for 20 min. Different sintering conditions may results in KNNs with varied properties. The studies of the structural properties of the prepared samples were done by X-ray diffraction (XRD) technique. It has been found that addition of MnO2 to KNNs and sintering at 1000 °C for 20 min and at 1050 °C for 10 min showed all the KNNs crystallization in tetragonal phase with nearly similar structural parameters. The electrical properties such as dielectric constant, dielectric loss and ac conductivity of the prepared samples were investigated using an impedance analyzer. The room temperature frequency variation of electrical properties showed a dispersive behavior for all the samples. The temperature variation of the dielectric properties showed an increase with the increase of temperature. The results of the various measurements are discussed in the paper. [ABSTRACT FROM AUTHOR]

The changes in the crystallographic parameters of Y 0.79- z Al z Yb 0.18 Er 0.03 NbO 4 powders prepared with varying Al content were determined by Rietveld refinement, and their effects on the up- (UC) and down-conversion (DC) spectra were studied. The findings confirmed that the Al3+, Yb3+, and Er3+ ions were completely incorporated at the Y3+ sites. The substitution of the small Al3+ ions led to the modification of the interatomic distance. As a result, the highest polyhedral distortion index of the YO8 dodecahedron (D YO) could be achieved at z = 0.2. Under infrared radiation, UC spectra demonstrated that a two-photon energy transfer (ET) UC process from Yb3+ to Er3+ was responsible for the green and red emissions, whose intensities increased dramatically by 160 and 166% at z = 0.2, respectively. This enhancement was a consequence of a large crystal-field asymmetry surrounding the Yb3+ and Er3+ ions, which resulted from the highest D YO at z = 0.2. In addition to D , the Yb‒Er interatomic distance was responsible for the enhanced UC emission, affecting the ET probability from Yb3+ to Er3+. Under 379 nm excitation, the DC green emission of Er3+ also showed the maximal intensity at z = 0.2 owing to the largest D YO. However, a correlation between the crystallographic variations and the DC emissions activated by [NbO 4 ]3- niobates could not be fully elucidated owing to the complexity of the emission mechanism. [ABSTRACT FROM AUTHOR]

The properties studying results of ceramics based on strontium, calcium and sodium niobates, which vary from the conditions of synthesis, sintering, and mechanical processing, are presented. The evolution of the grain structure of objects is traced depending on their phase filling during concentration changes in the composition and thermodynamic prehistory (preparation conditions). [ABSTRACT FROM AUTHOR]

Niobium-based oxides can be used in several applications due to a diverse set of properties. In this work, Na 2 Nb 2 O 6.H 2 O sodium niobate nanowires were obtained by hydrothermal synthesis at low temperature. Dehydrated sodium niobate (Na 2 Nb 2 O 6) and sodium niobate with perovskite structure (NaNbO 3) were obtained by submitting Na 2 Nb 2 O 6.H 2 O to heat treatment (350 °C and 500 °C, respectively). To obtain protonic niobates, sodium niobates were immersed in nitric acid in order to promote ion exchange reactions. From this procedure, protonic niobates (H 3 O) 2 Nb 2 O 6.H 2 O and (H 3 O) 2 Nb 2 O 6 were obtained. The sample NaNbO 3 did not undergo any transformation. Cyclic voltammetry tests carried out in a neutral aqueous solution 1 M Na 2 SO 4 showed a wide potential window for both niobates (sodium and protonic). However, the protonic niobate samples (H 3 O) 2 Nb 2 O 6.H 2 O and (H 3 O) 2 Nb 2 O 6 presented much higher current density values than the sodium niobates. This result can be related to a structural rearrangement that allowed a significant increase in the intercalation of sodium Na + ions from the electrolyte into the structure of these protonic niobates, when polarized. Therefore, in this work, it was demonstrated that it is possible to obtain protonic niobates from sodium niobates, as well as, it was verified the distinct electrochemical behavior between these materials. [ABSTRACT FROM AUTHOR]

In this study, Ba3SrNb2O9(s) was synthesized using conventional solid-state reaction route, characterized by powder XRD and SEM-EDAX. The standard molar enthalpy of formation of Ba3SrNb2O9(s) was determined measuring enthalpies of solution of Ba3SrNb2O9(s) in {PbO + B2O3} solvent (in 2:1 molar ratio) at T = 966 K using an oxide melt solution high temperature calorimeter. The enthalpy increment of Ba3SrNb2O9(s) was measured with same calorimeter. The heat capacity of the Ba3SrNb2O9(s) was also measured employing DSC. Based on the smoothed values of heat capacity, a table of thermodynamic data from 298 to 1000 K for Ba3SrNb2O9(s) was also constructed. [ABSTRACT FROM AUTHOR]

Phenol and its derivatives are present in effluents from several industrial processes, such as petroleum refining (produced water) and the pharmaceutical industry, and they are highly toxic. The present work elaborated a new catalyst for the removal of phenol and its derivatives. The photocatalyst was prepared by a simple method from the ammonium oxalate of niobium and nickel nitrate, resulting in heterostructures (principally NaNbO3/NaNb3O8 and a lesser amount of NiO) named NiNb. Platinum was deposited on this catalyst (NiNb/Pt catalyst), and its photocatalytic activity was tested on the degradation of phenol in seawater and distilled water, in the presence and absence of UV-C light (germicidal, λ = 254 nm), and with varying concentrations of platinum and varying pH of the solution. The catalyst was characterized by different techniques (SEM, EDS, DRS, XRD, TXRF, SBET,). The results of the study showed that the NiNb/Pt catalyst achieved 65% phenol removal in seawater and about 57% removal in distilled water. The reuse of the catalyst was also studied, and the photocatalytic mechanism was investigated by tests with scavenger agents and terephthalic acid.

Sodium niobate crystals doped with manganese ions, Na(NbMn)O3, were annealed in a nitrogen N2 flow at 600, 670, and 930 K. It was verified that simultaneous doping with Mn ions and annealing in nitrogen enhanced the photocatalytic features of sodium niobate. The transmission in the ultravioletvisible range was measured at room temperature. The absorbance edge is in the range from 3.4 to 2.3 eV. The optical band gap Egap¼1.2-1.3 eV was evaluated using the Tauc relation. Crystals annealed at 670K and 930K exhibited an additional shift of the absorption edge of ~20-40nm toward longer wavelengths. The optical energy gap narrowed as a result of the superimposed effect of Mn and N co-doping. The x-ray photoelectron spectroscopy test showed that N ions incorporated into the surface layer. The valence band consisted of O 2p states hybridized with Nb 4d, Mn 3d, and N 2s states. The disorder detected in the surroundings of Nb and O ions decreased due to annealing. The binding energy of oxygen ions situated within the surface layer was EB≈531 eV. The other contributions were assigned to molecular contamination. The contribution centered at 535.5 eV vanished after annealing at 600K and 670 K. The contribution centered at 534 eV vanished after annealing at 930 K. The N2 annealing partly removed carbonates from the surfaces of the samples. In the 480-950K range, the electric conductivity activation energy, Ea¼0.7-1.2 eV, was comparable with the optical Egap. The electric permittivity showed dispersion in the 0.1-800 kHz range that corresponds to the occurrence of defects. [ABSTRACT FROM AUTHOR]

The development of complex oxides that can be processed at temperatures at and below 350 °C is desirable for their integration onto polymeric substrates, enabling their use in flexible applications. Nanocomposite films consisting of a nanocrystalline fluorite related to delta-bismuth oxide in an amorphous matrix were prepared via chemical solution deposition. These solutions were batched with the composition Bi1.5Zn0.9Nb1.35Ta0.15O6.9. The nanocomposite had a relative permittivity of 50±2 and dielectric losses on the order of 0.03±0.01. For measurement frequencies of 1 kHz and 10 kHz, the nanocomposite demonstrated a breakdown strength of 3.8 MV/cm, and a roomtemperature energy storage density of approximately 40.2±1.7 J/cm3. To determine the suitability of the nanocomposite films for use in flexible applications, flexible nanocomposite films underwent repetitive compressive and tensile bending around a minimum bend diameter of 7mm, which corresponded to a strain of 0.10%. After bending the films 30 000 times, the energy storage density of the films was unchanged, demonstrating that nanocomposite bismuth zinc niobate tantalate films are suitable for flexible energy storage applications. [ABSTRACT FROM AUTHOR]