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K0.5Na0.5NbO3 (KNN) crystals have great application prospects due to their excellent piezoelectric properties, high Curie temperature, and environmental friendliness. Currently, KNN crystals grown by the seed-free solid-state crystal growth (SFSSCG) method exhibit relatively high dielectric loss. In order to reduce their dielectric loss, Cu, Bi and Mn co-doped KNN lead-free piezoelectric single crystals were prepared by the SFSSCG method. The effects of the CuO doping content on the structure and electrical properties of (1 − x)(0.996KNN–0.004BiMnO3)–xCuO crystals were systematically studied. The results show that an appropriate doping amount of CuO is beneficial for the growth of the crystals and the improvement of electrical properties. When the diameter of the billets is 40 mm, the maximum crystal size of 25 × 21 × 2 mm3 is obtained. All crystals have a typical perovskite structure almost with a single orthorhombic phase and are very compact almost without holes. The minimum average domain width of 276 nm is obtained for the crystal at x = 0.005. The KNN crystals exhibit normal ferroelectric characteristics and a space-charge-limited-conduction (SCLC) mechanism. The introduction of Cu2+ ions reduces the dielectric loss of the crystal and increases its piezoelectric and dielectric properties. The Cu, Bi and Mn co-doped KNN crystals achieve excellent comprehensive properties: d33 = 314 pC N−1, Pr = 29.9 μC cm−2, Ec = 10.1 kV cm−1, = 869 pm V−1, Qm = 56.8, Kt = 0.38, tan δ = 0.013 and TC = 409 °C. This provides a route to improve the electrical properties of KNN-based crystals. [ABSTRACT FROM AUTHOR]

In this study, it is reported that various properties can be selectively derived in a pure (K 0.5 Na 0.5)NbO 3 , KNN ceramics through optimizing the sintering temperature by the conventional sintering method. High piezoelectric, ferroelectric, and dielectric properties such as d 33 = 127 pC/N, P r = 31 μC/cm2, and ε r = 767 are obtained at the sintering temperature of 1100 °C. On the contrary, the specimen sintered at 1130 °C does not show high piezoelectric and ferroelectric properties, but it is translucent with a transmittance of 22% and 57% at the wavelength of 800 and 1600 nm respectively and shows a very high dielectric constant ε r of 881. The origin of the high piezoelectric constant owes to large remanent polarization and dielectric constant, and dense microstructure with uniform distribution of large grains with the conjunction of relatively large crystal anisotropy. On the other hand, dense microstructure with almost no porosity, highly compacted grain boundaries, uniform distribution of grains, and relatively low crystalline anisotropy are responsible for the translucency and large dielectric constant of the ceramic specimens. This study demonstrates that the lead-free KNN ceramic has the potential to show multiple noteworthy properties such as piezoelectric, ferroelectric, dielectric, and transparent properties. This work provides a pure KNN ceramic simultaneously with high piezoelectric and transparent characteristics prepared only by using the conventional sintering method at a moderate sintering temperature for the first time in the literature. [ABSTRACT FROM AUTHOR]

Abnormal grain growth (AGG) has been a common phenomenon during the ceramic or metallurgy processing since prehistoric times. However, usually it had been very difficult to grow big single crystal (centimeter scale over) by using the AGG method due to its so-called occasionality. Based on the AGG, a solid-state crystal growth (SSCG) method was developed. The greatest advantages of the SSCG technology are the simplicity and cost-effectiveness of the technique. But the traditional SSCG technology is still uncontrollable. This article first summarizes the history and current status of AGG, and then reports recent technical developments from AGG to SSCG, and further introduces a new seed-free, solid-state crystal growth (SFSSCG) technology. This SFSSCG method allows us to repeatedly and controllably fabricate large-scale single crystals with appreciable high quality and relatively stable chemical composition at a relatively low temperature, at least in (K 0.5 Na 0.5 )NbO 3 (KNN) and Cu-Al-Mn systems. In this sense, the exaggerated grain growth is no longer 'Abnormal' but 'Normal' since it is able to be artificially controllable and repeated now. This article also provides a crystal growth model to qualitatively explain the mechanism of SFSSCG for KNN system. Compared with the traditional melt and high temperature solution growth methods, the SFSSCG method has the advantages of low energy consumption, low investment, simple technique, composition homogeneity overcoming the issues with incongruent melting and high volatility. This SFSSCG could be helpful for improving the mechanical and physical properties of single crystals, which should be promising for industrial applications. [ABSTRACT FROM AUTHOR]

K 0.5 Na 0.5 NbO 3 (KNN)-based lead-free piezoelectric single crystals have been prepared by the Seed-Free, Solid-State Crystal Growth (SFSSCG) method, and the effects of MnO 2 doping on the structural and electrical properties were systematically investigated. The results showed that the MnO 2 -doping can promote the growth of K 0.5 Na 0.5 NbO 3 -BiAlO 3 (KNN-BA) single crystals and enhance its electrical properties. Furthermore, the size of the (1 - x)(KNN-BA)- x MnO 2 crystals reached the maximum value of about 18 × 17 × 2 mm3 at x = 0.005. Also, the color of the crystals did gradually change, from light yellow to dark brown, due to the addition of MnO 2. The XRD and refinement results showed that the addition of MnO 2 , in the range of 0 ≤ x ≤ 0.009, did not change the crystalline structure of the perovskite crystals. A two-phase perovskite crystalline structure was present in all crystals: an orthorhombic and a tetragonal phase. The content of the orthorhombic phase decreased, while the content of the tetragonal phase increased, with an increase in the MnO 2 content. In addition, the domains in the crystals were mainly composed of 180° ones and had a parallel lamellar structure. Also, the smallest average domain width was obtained for crystals with x = 0.003. These crystals had the largest piezoelectric constant of 568 pC/N and an excellent overall performance of d 33 = 568 pC/N, P r = 32.2 μC/cm2, Q m = 55.3, k t = 0.36, k p = 0.39, T C = 418 °C, ε r = 430, and tan δ = 0.015. • Compared with BiAlO 3 ceramics, single crystal exhibits more excellent electrical properties. • Using the Seed-Free, Solid-State Crystal Growth(SFSSCG) method, the process is simpler. • MnO 2 dopant promotes the growth of single crystal grains and the improvement of electrical properties. • The prepared KNN-BiAlO 3 single crystal has high piezoelectric properties. [ABSTRACT FROM AUTHOR]

K 0.5 Na 0.5 NbO 3 (KNN)-based lead-free piezoelectric single crystals have been prepared by the Seed-Free, Solid-State Crystal Growth (SFSSCG) method, and the effects of MnO 2 doping on the structural and electrical properties were systematically investigated. The results showed that the MnO 2 -doping can promote the growth of K 0.5 Na 0.5 NbO 3 -BiAlO 3 (KNN-BA) single crystals and enhance its electrical properties. Furthermore, the size of the (1 - x)(KNN-BA)- x MnO 2 crystals reached the maximum value of about 18 × 17 × 2 mm3 at x = 0.005. Also, the color of the crystals did gradually change, from light yellow to dark brown, due to the addition of MnO 2. The XRD and refinement results showed that the addition of MnO 2 , in the range of 0 ≤ x ≤ 0.009, did not change the crystalline structure of the perovskite crystals. A two-phase perovskite crystalline structure was present in all crystals: an orthorhombic and a tetragonal phase. The content of the orthorhombic phase decreased, while the content of the tetragonal phase increased, with an increase in the MnO 2 content. In addition, the domains in the crystals were mainly composed of 180° ones and had a parallel lamellar structure. Also, the smallest average domain width was obtained for crystals with x = 0.003. These crystals had the largest piezoelectric constant of 568 pC/N and an excellent overall performance of d 33 = 568 pC/N, P r = 32.2 μC/cm2, Q m = 55.3, k t = 0.36, k p = 0.39, T C = 418 °C, ε r = 430, and tan δ = 0.015. • Compared with BiAlO 3 ceramics, single crystal exhibits more excellent electrical properties. • Using the Seed-Free, Solid-State Crystal Growth(SFSSCG) method, the process is simpler. • MnO 2 dopant promotes the growth of single crystal grains and the improvement of electrical properties. • The prepared KNN-BiAlO 3 single crystal has high piezoelectric properties. [ABSTRACT FROM AUTHOR]

The Na0.5K0.5NbO3single crystal was successfully grown by a seed-free solid-state crystal growth method using super-low content of LiBiO3as a sintering aid. Microstructure, piezoelectric, ferroelectric and dielectric properties were investigated. The results show that well-paralleled lamellar ferroelectric ordering domains structure are present and no crack can be seen inside the single crystal. The best piezoelectric and dielectric properties (at 1 kHz) ofd33= 265 pC/N,Pr= 27.4 μC/cm2, ε = 738, tanδ = 0.04 appear atx= 0.40at% for (1-x)Na0.5K0.5NbO3-xLiBiO3single crystal. A higher remnant polarizationProf 36.3 μC/cm2were obtained atx= 0.45 at%. [ABSTRACT FROM AUTHOR]

Large Na0.5K0.5NbO3 ( NKN) piezoelectric single crystals were obtained by seed-free solid-state crystal growth method, which is a traditional sintering grain growth process, with LiBiO3 used as a sintering aid. The largest dimension of the single crystals obtained was 11 mm × 9 mm × 3 mm. In addition to the LiBiO3 doping content, temperature, and time effect of the crystal growth process was systematically investigated and considered from the kinetics point of view. With the assistance of Avrami analysis, parameters relevant to the crystal growth process were determined. Laue diffraction and transmission electron microscopy suggested an orthorhombic symmetry for the single crystalline structure. Dielectric-frequency-temperature measurements revealed an orthorhombic-tetragonal and tetragonal-cubic phase transition at 155°C and 405°C, respectively, both of which are typical of first-order transitions, and have a well-defined thermal hysteresis. Rayleigh analysis was performed regarding to the extrinsic reversible and nonreversible piezoelectric properties, and the result suggested a dominant intrinsic reversible piezoelectric contribution of 91.5% under E0 = 1 kV/cm AC amplitude. Such a single crystal growth process route is low cost and a relative simple preparation process. [ABSTRACT FROM AUTHOR]

Highlights: [•] Stepwise sulfidation methods were used on MoO3/CeO2–Al2O3 catalyst. [•] Stepwise sulfidation processes enhanced the methanation activity and stability. [•] Stepwise sulfidation decreased the damage to the textural structure of the catalyst. [•] Stepwise sulfidation decreased the damage to the CeO2 particles in the catalyst. [•] Stepwise sulfidation affected the CeO2 in the catalysts rather than the MoO3. [ABSTRACT FROM AUTHOR]

Highlights: [•] A comparative study of CeO2-Al2O3 prepared with different methods is carried out. [•] The catalysts whose support is prepared with DP exhibit the best activity. [•] CeO2 covered on the surface of support is favorable for the catalytic activity. [•] The formation of Al2(MoO4)3 and crystalline MoO3 does not favor the activity. [•] CeO2 layer decreases the negative effect of calcination temperature on catalysts. [ABSTRACT FROM AUTHOR]

Highlights: [•] Effect of sulfidation temperature on MoO3/CeO2–Al2O3 for methanation was studied. [•] Parts of CeO2 on the surface of Al2O3 served as the support of active phase. [•] Interaction between active phase and CeO2 improved the catalytic activity. [•] The sulfidation of unstable CeO2 enhanced the stability of catalyst. [ABSTRACT FROM AUTHOR]

Abstract: CeO2–Al2O3 supports were prepared by different methods and applied as MoO3/CeO2–Al2O3 catalysts for sulfur-resistant methanation. All characterization analyses of the catalysts indicated that when the Ce species are distributed in the bulk of the catalysts, they are favorable for the stability of the catalyst whereas when the Ce species are distributed on the surface of the catalyst, they are beneficial for the initial activity. Stepwise sulfidation is applied on MoO3/CeO2–Al2O3 catalyst to eliminate surface Ce species and migrate them to the inside of the catalyst, this also demonstrates that the Ce species distributed in the bulk of the catalysts are favorable for the stability. [Copyright &y& Elsevier]

Abstract: (1− x) (K0.44Na0.52Li0.04)(Nb0.84Ta0.1Sb0.06)O3 − x BiFeO3 (x =0, 0.002, 0.004, 0.006, 0.008, 0.01) lead-free piezoelectric ceramics were prepared by the conventional ceramic processing. The compositional dependence of the phase structure and the electrical properties of the ceramics were studied. A morphotropic phase boundary between the orthorhombic and tetragonal phases was identified in the composition range of 0.004< x <0.006. The ceramics near the morphotropic phase boundary exhibit a strong compositional dependence and enhanced piezoelectric properties. The ceramics with 0.6mol.% BiFeO3 exhibit good electrical properties (d 33 ∼246pC/N, k p ∼43%, T c ∼285°C, ɛ r ∼1871, and tan δ ∼1.96%). These results show that the (1− x) (K0.44Na0.52Li0.04)(Nb0.84Ta0.1Sb0.06)O3 − x BiFeO3 ceramic is a promising lead-free piezoelectric material for applications in different devices. [Copyright &y& Elsevier]

Abstract: Bi-doped ZnO thin films were grown on glass substrates by ratio frequency (rf) magnetron sputtering technique and followed by annealing at 400 °C for 4 h in vacuum (~10−1 Pa). The effect of argon pressure on the structural, optical, and electrical properties of the Bi-doped films were investigated. The XRD patterns show that the thin films were highly textured along the c-axis and perpendicular to the surface of the substrate. Some excellent properties, such as high transmittance (about 85%) in visible region, low resistivity value of 1.89×10−3 W cm and high carrier density of 3.45×1020 cm−3 were obtained for the film deposited at the argon pressure of 2.0 Pa. The optical band gap of the films was found to increase from 3.08 to 3.29 eV as deposition pressure increased from 1 to 3 Pa. The effects of post-annealing treatments had been considered. In spite of its low conductivity comparing with other TCOs, Bi-doping didn''t appreciably affect the optical transparency in the visible range of ZnO thin films. [Copyright &y& Elsevier]

Abstract: LiSbO3 doped and undoped 0.995 K0.5Na0.5NbO3–0.005BiFeO3 piezoelectric ceramics with high properties have been fabricated in air by the conventional ceramic processing. By adding LiSbO3 to K0.5Na0.5NbO3–BiFeO3 ceramics, the dielectric and piezoelectric properties evidently increase. The doped ceramics exhibit good electrical properties. The enhanced piezoelectric properties of the ceramics should be attributed to optimum LiSbO3 substitution and better microstructure with high density. Results show that LiSbO3 doped K0.5Na0.5NbO3–BiFeO3 lead-free piezoelectric ceramics are a promising lead-free piezoelectric material for applications in different devices. [Copyright &y& Elsevier]

(1− x)(0.95Na0.5K0.5NbO3–0.05LiSbO3)–xBiFeO3 solid-solution piezoelectric ceramics have been fabricated by conventional ceramic processing. A morphotropic phase boundary (MPB) between orthorhombic and tetragonal ferroelectric phases was identified around x =0.004. The ceramics near the MPB exhibit good electrical properties (d 33 =260pC/N−1, kp =51.5%, Tc =365°C, ρ =4.51gcm−3 and tan θ =2.00%). The results indicate that this ceramic is a promising lead-free piezoelectric material. [Copyright &y& Elsevier]

Abstract: Al–Ti codoped ZnO (ZATO) thin films were grown on glass substrates at room temperature by radio frequency (RF) magnetron sputtering technique and annealed under vacuum (∼10−1 Pa) at 400°C for 3h. The X-ray diffraction (XRD) patterns show that Al-doped ZnO (ZAO) and ZATO thin films are highly textured along the c-axis and perpendicular to the surface of the substrate. After annealing in a vacuum condition at 400°C for 3h, the lowest resistivity of 7.96 and 8.7×10−4 Ωcm are observed for ZATO and ZAO films, respectively. But after annealing in air, the resistivity of ZATO and ZAO is higher than 105 Ωcm. In the visible region, the ZAO films show the average transmittance of the order of 90%, while ZATO films were of the order of 75%, which illustrates that the additional Ti doping reduces the optical properties. The optical band gap was found to be 3.46eV for ZAO film and it increases to 3.53eV for ZATO films. [Copyright &y& Elsevier]

Abstract: Lead-free (Ba0.85Ca0.15)(Ti0.9Zr0.1)O3–x%CeO2(BCZT–xCe) piezoelectric ceramics have been prepared by the traditional ceramic process and the effects of CeO2 addition on their phase structure and piezoelectric properties have been studied. The addition of CeO2 significantly improves the sinterability of BCZT ceramics which results in a reduction of sintering temperature from 1540°C to 1350°C without sacrificing the high piezoelectric properties. X-ray diffraction data show that CeO2 diffuses into the lattice of BCZT and a pure perovskite phase is formed. SEM images indicate that a small addition of CeO2 greatly affects the microstructure. Main piezoelectric parameters are optimized at around x =0.04wt% with a high piezoelectric coefficient (d 33 =600pC/N), a planar electromechanical coefficient (k p =51%), a high dielectric constant (ɛ r =4843) and a low dissipation factor (tan δ =0.012) at 1kHz, which indicates that the BCZT–xCe ceramics are promising for lead-free practical applications. [Copyright &y& Elsevier]

Abstract: Lead-free (0.94− x)Na0.5K0.5NbO3–xBiNiO3–0.06LiSbO3 piezoelectric ceramics have been sintered at 1105°C by ordinary solid mixed oxide method. The phase transitional behavior and various electrical properties were investigated. All samples are typical ABO3 style perovskite structure. A morphotropic phase boundary between orthorhombic and tetragonal ferroelectric phases has been identified in the composition range of 0.002≤ x ≤0.004. Main piezoelectric parameters of these ceramics were optimized around x =0.002 with an enhanced piezoelectric constant d 33 of 240pCN−1, a planar electromechanical coefficient k p of 44%, a mechanical factor Q m of 38, and a Curie temperature T c of 360°C. These results indicate the materials studied have a promising future in a wide range of applications. [Copyright &y& Elsevier]

CaZrO 3 (CZ)-doped Na 0.5 K 0.5 NbO 3 (NKN)-based single crystals with 20 mm over were prepared by a seed-free solid-state crystal growth (SFSSCG) method. The microstructure, piezoelectric and dielectric properties of the crystal were investigated. The results show that the piezoelectric constant d 33 of this crystal is evidently enhanced up to 488 pC/N with the addition of CZ. Two dielectric anomalies appear at 391 and 149 °C, corresponding to the tetragonal → cubic and orthorhombic → tetragonal phase transition, respectively. There exists two domains (90° and 180°) in the crystal. These results show that this NKN-based crystal is a promising lead-free piezoelectric material for applications. [ABSTRACT FROM AUTHOR]

Abstract: Lead-free (1−x)(Ba0.85Ca0.15)(Ti0.9Zr0.1)O3−xBiYbO3 [(1−x)BCTZ−xBYO] piezoelectric ceramics in the range of BYO concentrations were prepared by the conventional oxide-mixed method, and the effect of BYO content on their microstructure, crystalline structure, density and electrical properties was investigated. A dense microstructure with large grain was obtained for the ceramics with the addition of BYO. The ceramics with x=0.1% exhibit an optimum electrical behavior of d 33~580pC/N, r~10.9Ω, k p~56.4%, and tan δ~1.12% when sintered at a low temperature of ~1350°C. When the measuring electric field is 40kV/cm, the well-saturated and square-like P–E loops for the ceramics were observed with P r~12.2μC/cm2 and E c~1.83kV/cm. [Copyright &y& Elsevier]

The phase relationships in the Gd-Co-Al ternary system at 500°C have been investigated mainly by X-ray diffraction, scanning electron microscopy, and energy dispersion spectroscopy. The existence of two ternary compounds GdCo0.74Al1.26 and Gd2Co2Al has been confirmed. Twenty-two single-phase regions (including solid solution regions of the binary compounds), 43 two-phase regions, and 22 three-phase regions were found to exist at this isothermal section. In this work, no new binary or ternary phase was found. [ABSTRACT FROM AUTHOR]

In this work, a novel pyroelectric catalysis technique is developed for decomposition of dye wastewater using the lead-free (K 0.5 Na 0.5)NbO 3 pyroelectric crystal catalyst under the environmental temperature variation. 91.2% of rhodamine B dye can be decomposed after (K 0.5 Na 0.5)NbO 3 pyroelectric catalyst undergoing 100 cold-hot 30–60 °C cycles. The catalytic activity can be obviously influenced by the poling electric field of catalyst materials. With the increase of the poling electric field from 0 to 4.5 kV/mm, the dye decomposition ratio correspondingly increases from 3.3% to 91.2%. The poling treatment is helpful to enhance the polarization of the (K 0.5 Na 0.5)NbO 3 crystal, which can also result in the increase of the pyroelectric coefficient, yielding to the enhancement of pyroelectric catalysis. The scavenger experiments are carried out, in which the main active species in the pyroelectric catalysis are found to be superoxide radicals, hydroxyl radicals and holes. The effects of various factors including dye concentration, catalyst dosage, pH and type of dyes on pyroelectric catalysis performance of (K 0.5 Na 0.5)NbO 3 are also investigated to obtain the optimum condition. The results of three consecutive recycling-utilization tests indicate that (K 0.5 Na 0.5)NbO 3 crystal possesses good chemical stability. With these advantages of high dye decomposition ratio and good recycling utilization, (K 0.5 Na 0.5)NbO 3 crystal is potential in developing the novel pyroelectric catalysis technique for decomposition of dye wastewater through utilizing the thermal energy from the environmental cold-hot temperature variation in future. Image 1 • Temperature variation-induced pyroelectric catalysis is discovered in (K 0.5 Na 0.5)NbO 3 crystal. • The pyroelectric catalysis of (K 0.5 Na 0.5)NbO 3 can be influenced through electric poling. • Electric field poling shows great potential in the preparation of pyroelectric catalysts. • It is desirable to realize dye wastewater purification through ultilizing cold-hot alternation. [ABSTRACT FROM AUTHOR]

BiFeO 3 –BaTiO 3 –Bi(Zn 0.5 Ti 0.5)O 3 + x Li 2 CO 3 (BFBT-BZT- x LC) lead-free piezoelectric ceramics with high Curie temperature and high temperature stability were made by refined solid-state reaction approach. More specifically, the phase transformation, microstructure, electric properties and high temperature stability of the ceramics were well studied. Experimental results demonstrate that piezoelectric properties and temperature stability of BFBT-BZT- x LC piezoelectric ceramics were significantly improved by adding Li 2 CO 3 sintering additives. What's more, when x = 0.3 mol% the ceramics sintered at 970 °C, the results show the optimal electrical properties with k p = 0.357, Q m = 35.687, tan δ = 0.043, d 33 = 184 pC/N. In particular, high Curie temperature (T C = 554 °C) and high depolarization temperature (T d = 530 °C, d 33 = 150 pC/N) were obtained. Therefore, the results show that BFBT-BZT- x LC ceramics are a promising high temperature lead-free piezoelectric ceramic material. • BiFeO 3 –BaTiO 3 –Bi(Zn 0.5 Ti 0.5)O 3 –Li 2 CO 3 ceramics exhibit high electric properties. • Excellent temperature stability with T c = 554 °C, T d = 530 °C. • High piezoelectric properties d 33 = 150 pC/N when T d = 530 °C. • The ceramics are ideal candidates for high temperature applications. [ABSTRACT FROM AUTHOR]

In this work, we report RuO 2 -loaded TiO 2 –MXene hybrid nanostructure as a promising photocatalyst possessing remarkable activity for photocatalytic nitrogen fixation in water at room temperature. The MXene was synthesized by HF etching of the precursor Ti 3 AlC 2 and used as the substrate for the growth of RuO 2 nanoparticles and TiO 2 through a hydrothermal reaction. The benign activity is mainly attributed to the synergetic effect among MXene, TiO 2 , and RuO 2 in photocatalytic ammonia synthesis by combining light harvesting and nitrogen activation. Image 1 • RuO 2 nanoparticles were hydrothermally loaded onto TiO 2 –Ti 3 C 2 T x MXene hybrid structure. • We explore their photocatalytic properties in reduction of nitrogen into ammonia. • Ultrasmall RuO 2 nanoparticles were hydrothermally synthesized on TiO 2 -loaded MXene. • The hybrid was used in photocatalytic nitrogen fixation under Xe-lamp irradiation. [ABSTRACT FROM AUTHOR]