Effects of SrTiO3 additives on the structure and microwave dielectric properties of Ba4.2Sm9.2Ti18O54 ceramics

The effects of SrTiO₃ additives on the microstructure and the dielectric properties of Ba_4.2Sm_9.2Ti₁₈O₅₄ (BST) materials have been investigated. The microstructure of BST doped with SrTiO₃ was analyzed using X-ray diffraction (XRD), scanning electron microscopy (SEM) and electron probe microanalyzer (EPMA). The XRD, SEM and EPMA results showed that small amounts of SrTiO₃ (less than 4 wt.%) could be accommodated in BST while a secondary metatitanate phase appeared in the samples with 8 wt.% SrTiO₃ added, the addition of SrTiO₃ increased the lower solubility limit (x values) of Ba_6?3xSm_8+2xTi₁₈O₅₄. The relative permittivities and the TC_f values showed an approximately linear increase with increasing additions of SrTiO₃. It was observed that near zero TC_f values could be achieved with the addition of SrTiO₃ to BST ceramics. With 4 wt.% SrTiO₃ addition and sintered at 1360 °C for 2 h, BST ceramics exhibited excellent dielectric properties: ?_r = 81.2, Q_f = 8470 GHz and TC_f = ?1.5 ppm/°C.     

Anti-reduction of Ti4+ in Ba4.2Sm9.2Ti18O54 ceramics by doping with MgO,Al2O3 and MnO2

The anti-reduction of Ti⁴⁺ ions in Ba_4.2Sm_9.2Ti₁₈O₅₄ (BST) ceramics at high sintering temperature over 1300 °C was investigated. MgO, Al₂O₃ and MnO₂ were added separately to suppress the reduction of Ti⁴⁺ ions so as to improve the microwave dielectric properties of BST ceramics. The microstructure of BST ceramics was analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). X-ray photoelectron spectroscopy (XPS) was used to study the electroconductivity of BST ceramics and valency changes of Ti ions. The results showed that MgO or Al₂O₃, when acting as an acceptor, could effectively suppress the reduction of Ti⁴⁺ ions and significantly improve the Q × f values of BST ceramics at the cost of dielectric constant. Meanwhile, MnO₂ as an oxidant had also improved the Q × f values but with no decrease in dielectric constant. Excellent microwave dielectric properties were achieved in Ba_4.2Sm_9.2Ti₁₈O₅₄ ceramics doped with 0.2 wt.% Al₂O₃ sintered at 1340 °C for 3 h: ?_r = 76.9, Q × f = 10,120 GHz and τ_f  = ?22.7 ppm/°C.     

Low‐firing and temperature stable microwave dielectric ceramics: Ba2LnV3O11 (Ln = Nd,Sm)

Low‐firing and temperature stable microwave dielectric ceramics of Ba₂LnV₃O₁₁ (Ln = Nd, Sm) were prepared by solid‐state reaction. X‐ray diffraction (XRD) and scanning electron microscopy (SEM) were used to investigate the phase purity, crystal structure, sintering behavior, and microstructure. The XRD patterns indicated that Ba₂LnV₃O₁₁ (Ln = Nd, Sm) ceramics belong to monoclinic crystal system with P2₁/c space group in the whole sintering temperature range (800°C ‐900°C). Both ceramics could be well densified at 880°C for 4 hours with relative densities higher than 96%. The Ba₂LnV₃O₁₁ (Ln = Nd, Sm) samples sintered at 880°C for 4 hours exhibited excellent microwave dielectric properties: ε_r = 12.05, Q × f = 23 010 GHz, τ_f = ?7.7 ppm/°C, and ε_r = 12.19, Q × f = 27 120 GHz, τ_f = ?16.2 ppm/°C, respectively. Besides, Ba₂LnV₃O₁₁ (Ln = Nd, Sm) ceramics could be well co‐fired with the silver electrode at 880°C.     

Microwave dielectric properties and thermally stimulated depolarization of Al-doped Ba4(Sm,Nd)9.33Ti18O54 ceramics

Ba₄(Sm_0.15Nd_0.85)_9.33Ti_18-zAl_3z/4O₅₄ (BSNT-zAl, 0.0 ≤ z ≤ 2.5) ceramics were prepared via a solid-state reaction, and the effects of Al doping on the microwave dielectric properties and defect behavior of the title compound were studied. X-ray diffraction (XRD) analysis and scanning electron microscopy (SEM) photographs suggested that Al ions successfully entered the lattice to form tungsten-bronze-like solid solutions. With a small amount of Al substitution, the relative dielectric constant (ε_r), and the temperature coefficient of resonant frequency (τ_f) values decreased, whereas the quality factor (Q × f) substantially increased by approximately 50%. The defect-related extrinsic dielectric loss was clarified via the thermally stimulated depolarization current (TSDC) technique. With Al doping, the TSDC relaxation of across-grain-boundary oxygen vacancies () vanished, whereas that of defect dipoles () appeared at relatively low temperatures. Therefore, in the BSNT-zAl ceramics, oxygen vacancies were more inclined to interconnect with to form defect dipoles. This could reduce the activity of and account for the notable improvement in the Q × f values. In particular, the excellent characteristics of ε_r = 67.33, Q × f = 16 530 GHz, and τ_f = +0.87 ppm/°C were achieved in the specimens with z = 1.5 sintered at 1350°C for 4 hours.     

Gas sensing and electrochemical properties of rare earthferrite,LnFeO 3 (Ln = Nd,Sm)

In this paper, nanostructured perovskite-type LnFeO₃ (Ln = Nd, Sm) oxides were synthesized by thermal treatment method (TTM). Characterization analysis conducted by X-ray diffraction (XRD), scanning electron microscopy (SEM) and micro-Raman spectroscopy, have confirmed the perovskite structure of the synthesized nanomaterials. To study the effects of Nd and Sm lanthanides substitution at the A-site on the chemical sensing performance, conductometric and electrochemical sensors based on the synthesized LnFeO₃ samples were fabricated. LnFeO₃-based conductometric and electrochemical sensors were tested for acetone and dopamine sensing, respectively. The data revealed that Nd and Sm in the A-position lead to a significant influence in the gas sensing and electrochemical properties of perovskite LnFeO₃ samples. In particular, it has been demonstrated the good gas sensing characteristics of SmFeO₃ for acetone gas (Response = R/R₀ = 8.3–20 ppm acetone at 200 °C), whereas NdFeO₃ displayed better performance as electrode for the electrochemical detection of dopamine reaching a low detection limit (LOD) of 270 nM at S/N = 3. The electrical and electrochemical characteristics of the perovskite LnFeO₃ samples were discussed in detail with respect to their chemical composition and microstructure.     

Microwave and terahertz properties of porous Ba4(Sm,Nd,Bi)28/3Ti18O54 ceramics obtained by sacrificial template method

Microwave and terahertz communications are increasingly significant, however, the lack of material information in terahertz band limits their development. Moreover, few lightweight materials with a high relative dielectric constant () are found suited for satellite communication and wearable devices. In this study, we developed lightweight porous Ba₄[(Sm_0.1Nd_0.9)_0.9Bi_0.1]_28/3Ti₁₈O₅₄ (BSNBT) ceramics exhibiting a total porosity ranging from 6.3% to 26.5% (bulk density ranging from 5.47 to 4.29 g/cm³) and relatively high ranging from 85.6 to 56.8, which were obtained by sacrificial template method using polymethyl methacrylate spheres (PMMAs) of varying average particle sizes, from 9 to 34 μm, as sacrificial materials. A high refractive index ranging between 7.5 and 8.9 and a low absorption coefficient of approximately 17 cm⁻¹ at 0.3 THz were obtained for the porous ceramics with different total porosities derived from PMMAs with average particle sizes of 9 and 19 μm. Furthermore, effective medium and Mie scattering theories were applied to understand the effects of porous structure on the dielectric properties in microwave and terahertz frequency ranges, respectively, owing to the different wavelengths in the BSNBT matrix. The results of this study suggest that introducing a porous structure can effectively exploit lightweight microwave dielectric ceramic materials and provide valuable information on their terahertz response mechanism.     

Effects of structural characteristics on microwave dielectric properties of (1 − x)Ca0.85Nd0.1TiO3–xLnAlO3 (Ln = Sm,Er and Dy) ceramics

Dependence of microwave dielectric properties on the structural characteristics of (1 − x)Ca_0.85Nd_0.1TiO₃–xLnAlO₃ (Ln = Sm, Dy and Er) ceramics were investigated as a function of LnAlO₃ content (0.05 ≤ x ≤ 0.25). For the specimens with SmAlO₃, a single phase with orthorhombic perovskite was obtained through the entire composition, however, Dy₂Ti₂O₇ and Er₂Ti₂O₇ were detected as a secondary phase along with the orthorhombic perovskite phase for the specimens with DyAlO₃ (x = 0.25) and ErAlO₃ (0.10 ≤ x ≤ 0.25), respectively. With an increase of LnAlO₃ content, the dielectric constant decreased due to the smaller ionic polarizability of LnAlO₃ than Ca_0.85Nd_0.1TiO₃. The temperature coefficient of the resonant frequency (TCF) decreased with LnAlO₃ content resulted from an increase of oxygen octahedral distortion.     

Crystal structure,spectra analysis and dielectric characteristics of Ba4M28/3Ti18O54 (M= La,Pr, Nd,and Sm) microwave ceramics

High dielectric constant Ba₄M_28/3Ti₁₈O₅₄ (M = La, Pr, Nd, and Sm) ceramics were synthesized via standard solid-state reaction route. All the samples possessed single-phase orthorhombic tungsten-bronze structure, and the unit cell volumes decreased monotonously when rare-earth ion changed from La to Sm. With the decreasing radius of rare-earth ions, the dielectric constant (ε_r) gradually decreased, which was correlated with the decrease of total ionic polarizability and blue shift of Raman vibration modes. The increase of the quality factor (Q × f) was associated with the increase of packing fraction and the decrease of FWHM of Raman vibration modes (A_g and B_1g). The temperature coefficient of resonant frequency (TCF) shifted in the negative direction, which was highly related to the decrease of the TiO₆ octahedral tilt angle. Infrared reflection (IR) spectroscopy analysis indicated that the infrared vibration modes between TiO₆ octahedron and A-site cation (M³⁺ and Ba²⁺) at low frequency dominated microwave dielectric polarization in the Ba₄M_28/3Ti₁₈O₅₄ ceramics.     

Sm掺杂对Ba_4La_(19.33)Ti_(18)O_(54)陶瓷结构和介电性能的影响分析

主要研究了不同Sm掺杂浓度对Ba4La19.33Ti18O54陶瓷的微波介电性能和微观结构的影响。首先利用常规固相反应技术制备了Sm含量y分别为0.0,0.1,0.3,0.5和0.7的五种Ba4(La1-ySmy)9.33Ti18O54陶瓷样品;室温下在0.3～3.0GHz频率范围内,利用网格分析仪测量了这些样品的介电常数和介电损耗因子;结果表明随着Sm掺杂含量的增大,样品介电损耗明显减小,而介电常数只有微小减少。当Sm掺杂含量y=0.5时,样品的介电性能最好。此外,还利用X射线衍射仪和扫描电子显微镜研究了样品的微观结构及随微波介电性能的变化。     

(1-x)Ba4Sm9.33Ti18O54-xCa0.61Nd0.26TiO3系微波介质陶瓷

采用固相合成法制备了(1-x)Ba4Sm9.33Ti18O54-xCa0.61Nd0.26TiO3[(1-x)BST-xCNT]系微波介质陶瓷.探讨了组成、烧结温度对微波介质陶瓷结构、介电性能的影响.x＜0.6时,(1-x)BST-xCNT陶瓷为正交结构的新型钨青铜单相.x≥0.6时,相继出现了第二相Sm2Ti2O7和钙钛矿相,最终形成钙钛矿单相.微波介质陶瓷的介电常数ε随x的增大持续升高,品质因子Qf值则先增大后迅速减小再急剧增大.1 325～1 350 ℃烧结样品的微波介电性能达到最佳:x=0时,ε=75,Qf=8985GHz,谐振频率温度系数τf=-8.2×10-6/℃;x=0.2时,ε=75,Qf=9 552GHz,τf=-14.4×10-6/℃;x=1时,ε=108.9,Qf=14919GHz,τf=236.2×10-6/℃.     

Densification,microstructural evolution and dielectric properties of Ba6 − 3x(Sm1 − yNdy)8 + 2xTi18O54 microwave ceramics

Utilizing different rare-earth cations R³⁺ to the Ba_6 − 3xR_8 + 2xTi₁₈O₅₄ compounds is one of effective route to tailor the dielectric constant, quality factor and temperature coefficient of frequency. In this study, densification, microstructural evolution, and microwave dielectric properties of Ba_6 − 3x(Sm_1 − yNd_y)_8 + 2xTi₁₈O₅₄ compound, with x ranging from 0.3 to 0.7; and y from 0 to 1.00, were investigated. The ceramics with x = 0.7 [Ba_3.9(Sm_1 − yNd_y)_9.4Ti₁₈O₅₄] has a higher densification compared with others, due to the formation of vacancy, in the perovskite-like tetragonal cavity of the tungsten bronze-type framework structure. Differential thermal analysis and density results show that the densification of Ba_6 − 3x(Sm_yNd_1 − y)_8 + 2xTi₁₈O₅₄ ceramics during sintering is primarily resulting from the solid state sintering process. The phase homogeneity for the Ba_6 − 3x(Sm_0.5Nd_o.5)_8 + 2xTi₁₈O₅₄ system is at least extended in the range of x between 0.3 and 0.7. Combining different rare-earth cations appears not alter the single phase range in tungsten bronze-type Ba_6 − 3xR_8 + 2xTi₁₈O₅₄ ceramics. The size of the columnar-grain in the microstructure increases with increasing the Nd/Sm ratio as well as the x value. Dielectric constant changes from 91.0 to 84.2 as the x increases from 0.3 to 0.7. Variation of the Nd/Sm ratio allows one to control the τ_f value to the nearly 0 ppm/°C.     

Relaxor nature in Ba5RZr3Nb7O30 (R = La,Nd, Sm) tetragonal tungsten bronze new system

Ba₅RZr₃Nb₇O₃₀(R = La, Nd, Sm) lead‐free relaxor ferroelectrics were prepared by a standard solid‐state reaction process, and the influence of A and B site ion occupation on the dielectric characteristics especially the relaxor nature were investigated systematically. Tetragonal tungsten bronze structure with space group P4/mbm was determined for all compositions, ion cross distribution by Ba²⁺ and R³⁺ in A1 site was observed, while A2 site was only occupied by Ba²⁺. Selected area electron diffraction patterns confirmed the existence of incommensurate superlattice modulation. Furthermore, temperature and frequency dependences of the dielectric properties showed a broad permittivity peak with strong frequency dispersion, following well the Vogel‐Fulcher relationship. The maximum dielectric constant temperature increased gradually with decreasing A1 site ion size. Slim P‐E hysteresis loops were obtained at room temperature for all compositions. Meanwhile, micro ferroelectric domains were observed in Ba₅SmZr₃Nb₇O₃₀. For Ba₄R₂Zr₄Nb₆O₃₀ and Ba₅RZr₃Nb₇O₃₀ (R = Nd, Sm), the transition from normal ferroelectric to relaxor behavior originates from the increased t_A1, which is a result of cross distribution at A1 site. Compared with Ba₅RTi₃Nb₇O₃₀, Zr substitution at B site enhances the relaxor nature.     

Microwave dielectric properties of tungstenbronze type like (Ba1−αSrα)6−3xR8+2xTi18O54 (R = Sm,Nd) solid solutions

Tungstenbronze type like Ba_6−3xR_8+2xTi₁₈O₅₄ (R = Sm or Nd) dielectric ceramics reveal high quality factor Q·f as well as high dielectric constant ɛ_r. We have investigated the effect of Sr substitution for Ba ions on the microwave dielectric properties of the compounds. (Ba_1−αSr_α)_6−3xR_8+2xTi₁₈O₅₄ (R = Sm or Nd) ceramics were prepared in the composition ranges of x = 0–0.2 and α = 0–0.312 and the microwave dielectric properties were investigated. (Ba_1−αSr_α)_6−3xSm_8+2xTi₁₈O₅₄, where x = 0.1 and α = 0.298, and (Ba_1−αSr_α)_6−3xNd_8+2xTi₁₈O₅₄, where x = 0.2, α = 0.296 revealed remarkably higher Q·f value among the solid solutions, indicating that Q·f increased with substituting Sr ions into Ba ions at the rhombic A1-site. This fact suggests that relaxation of local distortions at the A1-sites is closely related to improvement of Q·f.     

Near-infrared luminescent properties of Ln:LaGdZr2O7 (Ln = Nd,Yb) transparent ceramics for solid-state laser applications

Via a facile solid reactive method, transparent Ln_0.1La_0.9GdZr₂O₇ (Ln = Nd, Yb) ceramics were successfully fabricated for the first time. The highest in-line transmittances of Nd:LaGdZr₂O₇ and Yb:LaGdZr₂O₇ ceramics reached 68% and 69%, respectively, at 1100 nm. The microstructure and crystal structure of Ln_0.1La_0.9GdZr₂O₇ transparent ceramics were fully investigated, indicating that the solid reactive technique is a good method of industrially fabricating Ln_0.1La_0.9GdZr₂O₇ transparent ceramics. The PL spectra demonstrated that Ln_0.1La_0.9GdZr₂O₇ ceramics can effectively be excited at 808 nm and 976 nm, which correlates with the widely applied output wavelengths of AlGaAs and InGaAs laser diodes. The luminescence decay curves were also studied, showing that the average fluorescence lifetimes of Nd_0.1La_0.9GdZr₂O₇ and Yb_0.1La_0.9GdZr₂O₇ transparent ceramics was 355 μs and 663 μs, respectively. Combined with its high temperature resistance and good mechanical strength, Ln_0.1La_0.9GdZr₂O₇ (Ln = Nd, Yb) transparent ceramics can have potential applications in Nd/Yb solid-state laser construction.     

Dielectric anisotropy and sinterability improvement of Ba4Nd9.33Ti18O54 textured ceramics

The 〈0 0 1〉-textured Ba₄Nd_9.33Ti₁₈O₅₄ (BNdT) ceramics were fabricated by templated grain growth process. Acicular particles prepared using K₂SO₄ molten salt were used as template and aligned by tape casting in the equiaxed BNdT powder. Crystalline phases of sintered specimen exhibited {h k 0} and {0 0 1} development in the plane of parallel and perpendicular to the casting direction, respectively. The formation of a slight amount of secondary phase in the template particles and the compositional deviation inhibited the densification and texture development for BNdT. To improve the sinterability, the composition shifted from BNdT to Ba₂Ti₉O₂₀ (B2T9) rich side slightly in BaONd₂O₃TiO₂ ternary system, which enables to promote a liquid phase during the sintering, was examined as a matrix phase. Resultant ceramics including B2T9-rich matrix phase displayed high density and large dielectric anisotropy. Temperature dependence of dielectric constant showed negative and positive behavior between the direction of parallel and perpendicular to the 〈0 0 1〉-textured BNdT. Near-zero temperature coefficient of resonant frequency (τ_f) in TE_0 1 1 mode was obtained in the textured ceramics with the degree of {0 0 1} orientation of approximately 0.37 on the disk plane. The exceptional temperature behavior of BNdT made it possible to control the τ_f over the wide range by the combination of dielectric anisotropy.     

Calcium-magnesium-alumina-silicate (CMAS) resistance characteristics of LnPO4 (Ln = Nd,Sm, Gd) thermal barrier oxides

Calcium-magnesium-alumina-silicate (CMAS) attack has been considered as a significant failure mechanism for thermal barrier coatings (TBCs). As a promising series of TBC candidates, rare-earth phosphates have attracted increasing attention. This work evaluated the resistance characteristics of LnPO₄ (Ln = Nd, Sm, Gd) compounds to CMAS attack at 1250 °C. Due to the chemical reaction between molten CMAS and LnPO₄, a dense, crack-free reaction layer, mainly composed of Ca₃Ln₇(PO₄)(SiO₄)₅O₂ apatite, CaAl₂Si₂O₈ and MgAl₂O₄, was formed on the surface of compounds, which had positive effect on suppressing CMAS infiltration. The depth of CMAS penetration in LnPO₄ (Ln = Nd, Sm, Gd) decreased in the sequence of NdPO₄, SmPO₄ and GdPO₄. GdPO₄ had the best resistance characteristics to CMAS attack among the three compounds. The related mechanism was discussed based on the formation ability of apatite phase caused by the reaction between molten CMAS and LnPO₄.     

Three dimensional lanthanide-organic frameworks containing tetranuclear Ln (Ln = La,Nd) cluster secondary building blocks

The hydrothermal reactions of Ln₂O₃, o-phthalic acid (H₂L₁) and N,N’-Piperazine(bis-methylene phosphonic acid) hydrochloride (H₄L₂·HCl) yielded two three dimensional (3D) lanthanide-organic frameworks formulated as [Ln₄(L₁)₂(H₂L₂)₃(H₃L₂)₂]·18H₂O (Ln = La, 1; Nd, 2). Single-crystal X-ray diffraction revealed that they are isostructural. They feature 3D open framework structures containing rarely observed centrosymmetric tetranuclear lanthanide sub-building units (SBU). The photoluminescence property of 2 has been investigated, and it shows strong solid-emissions in the near-infrared region at room temperature.     

Sm掺杂对Ba4La19.33Ti18O54陶瓷结构和介电性能的影响分析

主要研究了不同Sm掺杂浓度对Ba4La19.33Ti18O54陶瓷的微波介电性能和微观结构的影响。首先利用常规固相反应技术制备了Sm含量y分别为0、0．1、0．3、0．5和0．7的5种Bat（La1-y,Smy）9.33T18O54陶瓷样品;室温下在0．373．0GHz频率范围内,利用网格分析仪测量了这些样品的介电常数和介电损耗因子;结果表明随着Sm掺杂含量的增大,样品介电损耗明显减小,而介电常数只有微小减少。当Sm掺杂含量y=0．5时,样品的介电性能最好。此外,还利用X射线衍射仪和扫描电子显微镜研究了样品的微观结构及随微波介电性能的变化。     

Effects of Re2O3 (Re = La,Nd, Y and Yb) addition in hot-pressed ZrB2–SiC ceramics

ZrB₂–20 vol% SiC composites with 3 vol% Re₂O₃ rare-earth oxide (Re = La, Nd, Y or Yb) were hot pressed to near full-density at 1900 °C. The La₂O₃ and Nd₂O₃ additions not only caused the formation of an amorphous grain boundary phase and enhanced densification, but also resulted in substantial ZrB₂ and SiC grain growth. In contrast, the Y₂O₃ and Yb₂O₃ additions resulted in the formation of crystalline (Y/Yb)₂Zr₂O₇ and enhanced densification without ZrB₂ and SiC grain growth. The hardness was improved by the rare-earth oxide addition, especially with Y₂O₃ and Yb₂O₃. The La₂O₃ and Nd₂O₃ only had a minor effect on the fracture toughness, whereas the Y₂O₃ and Yb₂O₃ additions increased the fracture toughness. The type of Re₂O₃ addition was found to influence the nature of the grain boundary and the concomitant fracture and toughening mechanisms.