Sintering behavior and microwave dielectric properties of （1-x）CaTiO_3-xLaAlO_3 ceramics

The sintering behavior,microstructure and microwave dielectric properties of (1–x)CaTiO3–xLaAlO3 (x=0.1,0.3,0.5,0.7,0.9,respectively) ceramics were investigated systematically by thermogravimetry-differential thermal analysis (TG-DSC),X-ray diffraction (XRD),scanning electron microscopy (SEM) and a network analyzer.The result showed that forming temperature of the perovskite type crystal increased with increasing of x value.0.9CaTiO3-0.1LaAlO3 ceramics were sintered well from 1 400 to 1 550 oC,its bulk density increased with sintering temperature,and microwave dielectric properties of the ceramics at 1 400 oC was shown as follows: relative dielectric constant εr= 45.1,Q×f= 46 087 GHz and τf=–14.1×10–6/oC,respectively.But 0.7CaTiO3-0.3LaAlO3 ceramics were sintered well only when sintering temperature rose to 1 500 oC.(1–x)CaTiO3–xLaAlO3 (x=0.5,0.7 and 0.9,respectively) were not sintered well up to 1 550 oC and the sintered samples exhibited porous characteristic and with low bulk density.     

Effect of Nd2O3 doping on the electrical properties of Ba0.96Ca0.04Ti0.90Sn0.10O3 ceramics

The Ba_(0.96)Ca_(0.04)Ti_(0.90)Sn_(0.10)O_3-xNd_2 O_3(x = 0-0.08%) ceramics were prepared via traditional solid-state sintering method. The influences of Nd3+ substitution on the phase structure, dielectric properties,piezoelectric and ferroelectric properties of the ceramics were investigated. All the samples possess pure BaTiO_3-type perovskite structure. MPB with orthorhombic and tetragonal phase coexist at around x = 0.03-0.04. Nd~(3+) doping decreases both Tc and T_(O-T) to lower temperature. All the samples exhibit an intermediate state with the coexistence of ferroelectric and diffuse relaxor ferroelectric behavior with the addition of Nd~(3+). The electric properties of the ceramics were optimized at x = 0.03 with d33, K_p, ε_r and P_r values of 545 pC/N, 51.9%, 24,412 and 10.74 μC/cm~2.     

Relaxor behavior and superior ferroelectricity of Y2O3-doped (Ba0.98Ca0.02) (Ti0.94Sn0.04Zr0.02)O3 lead-free ceramics

To upgrade the electric properties of lead-free piezoceramics, (1–x)(Ba_0.98Ca_0.02Ti_0.94Sn_0.04Zr_0.02)O₃-xY₂O₃ (abbreviated as (1–x)BCTSZ-xY, x = 0 mol%, 0.02 mol%, 0.04 mol%, 0.06 mol%, 0.08 mol% and 0.1 mol%) ceramics were successfully synthesized by traditional solid-state sintering method. The phase structure and microstructure of ceramics were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and piezoresponse force microscopyeramics (PFM). The electric properties of ceramics were researched through piezoelectric, dielectric and ferroelectric test instruments. The results show that all samples have pure perovskite structure and favorable electric properties. The optimal electric properties which especially include superior ferroelectric properties are gained when Y₂O₃ content is 0.06 mol% (d₃₃ = 419 pC/N, k_p = 52%, T_c = 89.5 °C, ε_r = 26900, tanδ = 2.86%, P_r = 14.41 μC/cm², E_c = 1.8 kV/cm). Moreover, the temperature-dependent dielectricity of samples shows apparent relaxor behavior under different frequencies. The Curie–Weiss law further proves that all samples are typical relaxor ferroelectrics, and the relaxor degree of samples decreases with increase of Y₂O₃ content. In conclusion, Y₂O₃ plays a significant role in enhancing electric properties of BCTSZ ceramics.     

Microwave dielectric properties of Ba6-3xLa8+2x(Ti1-zZrz)18O54(x=2/3)ceramics

Zr substitution for Ti was investigated to modify the dielectric properties of Ba6-3xLa8+2xTi18O54(x=2/3) ceramics.A single-phase solid solution with tungstenbronze-like structure was formed in the range of 0     

ZnO-B_2O_3掺杂陶瓷的微观结构和微波介电性能

研究了ZnO-B_2O_3(ZB_2)对(Ca_(0.254)Li_(0.19)Sm_(0.14))TiO_3陶瓷的烧结行为和微波介电性能的影响。结果表明:ZnO-B_2O_3添加质量分数为3%时,试样的相对密度达到最大值;烧结温度从1 300℃降低到1 100℃时,试样的微波介电性能没有衰减。添加3%ZB_2(质量分数)的(Ca_(0.254)Li_(0.19)Sm_(0.14))TiO_3陶瓷在1 100℃烧结3 h呈现出较好的微波介电性能,介电常数ε_r=108.2,品质因数Q_f=6 545 GHz,共振频率温度系数τf=6.5×10~(-6)/℃,表明ZB_2是一种有效改善(Ca_(0.254)Li_(0.19)Sm_(0.14))TiO_3陶瓷致密性和微波介电性能的烧结助剂。     

Role of localized phonon vibration in luminescence performance of Pr doped Ba(Mg0.28Zr0.16Ta0.56)O3 transparent ceramics

Oxygen-assisted high temperature solid-state reaction approach was employed for the fabrication of Pr activated Ba(Mg_0.28Zr_0.16Ta_0.56)O₃ transparent ceramic phosphor. Retiveld refinement of X-ray diffraction pattern was carried out to reveal the lattice parameters and crystal structural information. Under the blue-light excitation of λ_ex = 473 nm, the phosphor exhibits a sharp intense red emission centered at 645 nm, accompanied by several other weak peaks. PL evolution with temperature shows a significant luminescence quenching behavior, and the underlying multi-phonon interaction with optical center is revealed by proposing an unprecedent theoretical calculation work. Such a phonon effect is further confirmed from the red-shift of peak position with temperature, and the involved phonon energy of 50.7 meV is determined from Raman scattering measurement. More interestingly, the fitted results of transient-state PL spectra show a fluctuation of luminescence lifetime at various temperatures, further indicating a significant effect of phonon vibration in the system.     

Growth and property enhancement of Er3+-doped 0.68Pb(Mg1/3Nb2/3)O3-0.32PbTiO3 single crystal

Er~(3+)-modified 0.68 Pb(Mg_(1/3)Nb_(2/3))O_3-0.32 PbTiO_3(PMN-32 PT) single crystals were grown by using the flux method. The growth mechanism of the crystal and influences of Er~(3+) ions on phase structure,electrical and optical properties were investigated. Results reveal that the crystals are still pure perovskite structure with Er3+ ions doping, but lattice enlarges slightly. The coercive electric field is increased from 4.83 to 6.37 kV/cm for [100]-oriented crystals comparing to undoped PMN-32 PT single crystals.Moreover, the crystal exhibits upconversion emission properties. Green(531 and 552 nm) and red(670 nm) emission bands are recorded under the excitation of 980 nm diode laser, which correspond to the ~2 H_(11/2)→~4 I_(15/2), ~4 S_(3/2)→~4 I_(15/2) and ~4 F_(9/2)→~4 I_(15/2) transitions of Er~(3+) ions. Our results show the feasibility of using this crystal in photoelectric multifunctional devices.     

Electrical and dielectric properties of Ni0.5Co0.5GaxFe1.8-xO4(x≤1.0)spinel ferrite microspheres

Microspheres of Ni_0.5 Co_0.5Ga_xFe_2-xO₄(x≤1.0) microsphere spinel ferrites(NiCoGaFe-MSFs) and carbon spheres were prepared via a hydrothermal technique.The micro structure of microspheres was investigated through scanning and transmission electron microscopy(SEM and TEM),respectively,and X-ray diffraction(XRD).The electrical and dielectric properties of NiCoGaFe-MSF at temperatures ranging from20 to 120℃(between 293,1× 10³ and 393.1...     

掺杂不同质量分数Y_2O_3、MgO对Al_2O_3陶瓷显微结构及介电性能的影响

利用放电等离子烧结技术制备了不同质量分数Y_2O_3单独掺杂及不同质量分数Y_2O_3、MgO共同掺杂的Al_2O_3陶瓷,研究了烧结助剂掺杂质量分数对Al_2O_3陶瓷显微结构及介电性能的影响。结果表明,孔隙率是影响Al_2O_3陶瓷介电性能的主要因素;单独掺杂质量分数为0.25% Y_2O_3时,Al_2O_3陶瓷得到最优的介电性能,介电常数(ε_r)为9.5±0.2,介质损耗(tanδ)稳定在10~(-3)数量级以内;同时掺杂Y_2O_3和MgO能进一步改善其介电性能,当两者质量分数均为0.25%时,得到最优值,介电常数(ε_r)为10.3±0.2,介质损耗(tanδ)稳定在8×10~(-4)以下。     

CuTa_2O_6掺杂Ba(Zn_(1/3)Ta_(2/3))O_3基微波陶瓷烧结动力学及微波性能

结合烧结动力学模型和微观形貌观察,研究未掺杂和掺杂CuTa_2O_6的Ba(Zn_(1/3)Ta_(2/3))O_3陶瓷在1 270~1 520℃温度范围内的致密化过程和烧结动力学机理。结果表明:在1 150℃以上烧结,随温度升高,Ba(Zn_(1/3)Ta_(2/3))O_3的烧结机制从体积扩散向晶界扩散转变。掺杂0.25%CuTa_2O_6可显著加快Ba(Zn_(1/3)Ta_(2/3))O_3陶瓷的烧结致密化过程,在显著降低烧结温度的同时,可大幅缩短烧结时间并有效地促进B位的有序化。掺杂Ba(Zn_(1/3)Ta_(2/3))O_3陶瓷在1370℃烧结12h即可获得96%的相对密度,在1 370℃烧结12 h后的介电常数(εr)和品质因数(Q·f)分别约为29.4和985 35;相比较,未掺杂Ba(Zn_(1/3)Ta_(2/3))O_3在1 520℃烧结12 h的εr和Q·f分别只有27.4和68 147。掺杂Ba(Zn_(1/3)Ta_(2/3))O_3陶瓷经1 520℃烧结48 h的εr和Q·f分别约为28.2和103 131。     

Optical properties and irradiation resistance of novel high-entropy oxide glasses La2O3-TiO2-Nb2O5-WO3-M2O3(M=B/Ga/In)

A new class of high-entropy oxide glasses 20LaO_3/2-20TiO₂-20NbO_5/2-20WO₃-20MO_3/2(M=B/Ga/In)were designed and successfully fabricated by aerodynamic containerless processing.The results show that one can control the properties and increase the functionality of glass by changing the type of M.The Vicker’s hardness reaches the highest value of 6.45 GPa for glass M=B.The best thermal stability and the glass forming ability,measured using the gla...     

Photoluminescent properties of Ca2Gd8(SiO4)6O2: Dy3+ phosphor films prepared by sol-gel process

There are growing interests on phosphor thin films owing to their potential application in high-resolution devices such as cathode ray tubes and flat panel display devices. The solution-based sol-gel method is one of the most important techniques for the synthesis of vari-ous functional coating films. Compounds with the apatite structure are very suitable host lattices for various luminescent ions. Ca2RE8(SiO4)6O2 ( RE=Y, Gd, La ) is a kind of ternary rare-earth-metal silicate with oxyapatite structure, which has been used as host mate-rial for the luminescence of various rare earth and mercury-like ions. In this article, Ca2Gd8(SiO4)6O2:Dy3 phosphor films were dip-coated on quartz glass substrates through the sol-gel process. X-ray diffraction (XRD), atomic force microscopy (AFM), photoluminescence (PL) spectra, as well as lifetimes were used to characterize the resulting films. AFM study revealed that the phosphor films consisted of homoge-neous particles. The Dy3 showed its characteristic emission in crystalline phosphor films, i.e., 4F9/2–6H15/2 and 4F9/2–6H13/2.     

Thermoelectric properties of Sr0.9La0.1TiO3 and Sr2.7La0.3Ti2O7 with 15%Ag addition

15%Ag-added cubic perovskites Sr0.9La0.1TiO3 and Ruddlesden-Popper （RP） phases Sr2.7La0.3Ti2O7 were fabricated via hydrothermal synthesis, cold pressing and high-temperature sintering. The structure and thermoelectric properties were also investi-gated for all samples. The results indicated that Ag precipitated as a second phase. Ag addition made electrical conductivity and ab-solute Seebeck coefficient enhanced, as a result, the ZT values were enhanced both for two series. Compared with cubic perovskite, RP phase was subjected to smaller impact by Ag addition. The reasons for enhancing ZT value and the different impact for two series by Ag addition were also discussed.     

A single-phase full-color phosphor Sr2Ca2La(PO4)3O:Eu2+,Tb3+,Mn2+: Photoluminescence and energy transfer

A single-phase full-color emitting phosphor Sr₂Ca₂La(PO₄)₃O:Eu²⁺,Tb³⁺,Mn²⁺ was synthesized by the high temperature solid-state method. The phase formation, luminescence properties, thermal stability, and energy transfer from Eu²⁺ to Tb³⁺ and Eu²⁺ to Mn²⁺ in Sr₂Ca₂La(PO₄)₃O were investigated in details. Tunable emission color from blue to blueish green or orange can be observed under 365 nm near-ultraviolet excitation based on the energy transfer from Eu²⁺ to Tb³⁺ or Mn²⁺ ions by varying the ratio of Eu²⁺/Tb³⁺ or Eu²⁺/Mn²⁺ ions. White light was obtained with chromaticity coordinates of (0.3558, 0.3500) in the Sr₂Ca₂La(PO₄)₃O:0.04Eu²⁺,0.08Tb³⁺,0.40Mn²⁺ phosphor, suggesting their potential applications in white light emitting diodes.     

Multiferroic properties of Bi5.75R0.25Fe1.4Ni0.6Ti3O18 (R = Eu,Sm, Nd,Bi and La) ceramics

An improved technique was used to prepare the ceramic samples of Bi_5.75R_0.25Fe_1.4Ni_0.6Ti₃O₁₈(BRFNT,R=Eu,Sm,Nd,Bi,and La).The five-layer Aurivillius phase of the samples was confirmed by X-ray diffraction(XRD)without detectable impurities.BRFNT samples exhibit the pseudo-tetragonal except the orthorhombic BSmFNT samples.The characteristic plate-like morphology was revealed by field emission transmission electron microscopy(FETEM)images.At ambient tempe rature,all the samples present both ferroelectric and magnetic properties and BEuFNT shows the best ferroelectric behavior with its remanent polarization as high as 14.9μC/cm²under 155 kV/cm,which is three times higher than that of Bi_5.75R_0.25Fe_1.4Ni_0.6Ti₃O₁₈.Moreover,the remanent magnetization of BEuFNT is increased up to 1.20 emu/g compared to that of Bi_5.75R_0.25Fe_1.4Ni_0.6Ti₃O₁₈which is only 0.53 emu/g.With increasing radius of the introduced A-site ions,the ferroelectric phase transition temperature(T_CE)is decreased while the magnetic phase transition temperature(T_CM)fluctuates.The decrease in both T_CEand T_CM corresponds to the upward shift of the related Raman modes and vice versa,indicating that the T_CEand the T_CM depend not only on the t factor,but also on the strength of the covalent bonds.     

Sintering effect on ageing behavior of rare earths （Pr6O11-Er2O3-Y2O3 ）-doped ZnO varistor ceramics

The electrical properties and ageing behavior of the rare earths (Pr6O11-Er2O3-Y2O3)-doped ZnO varistor ceramics were systematically investigated at sintering temperature range of 1335-1350°C. With an increase in the sintering temperature, the sintered density increased from 5.41 to 5.64g/cm3 and the average grain size increased from 5.8 to 7.9μm. The varistor properties and ageing behavior were significantly affected by small sintering temperature range of 1335-1350°C. The breakdown field noticeably decreased from 5767 to 3628V/cm with an increase in the sintering temperature. The varistor ceramics exhibited the highest nonlinear coefficient (43.2) at the sintering temperature of 1340°C. The varistor ceramics sintered at 1350°C exhibited a surprisingly excellent stability by exhibiting 0.3% in the variation rate of the breakdown field and 0.3% in the variation rate of the nonlinear coefficient for ageing stress of 0.95 E1mA/150°C/24 h.     

Magnetic properties and magnetocaloric effects of manganite (La0.8Ho0.2)2/3Ca1/3MnO3 and (La0.5Ho0.5)2/3Ca1/3MnO3

We reported the magnetic properties and magnetocaloric effects (MCE) of (La_0.8Ho_0.2)_2/3Ca_1/3MnO₃ and (La_0.5Ho_0.5)_2/3Ca_1/3MnO₃ nanoparticles by sol-gel technique. With this method, we were able to obtain the samples with particle diameters ranging from 50 to 200 nm. In the (La_1-xHo_x)_2/3Ca_1/3MnO₃ compound, an external magnetic field induced a magnetic transition from an paramagnetic phase to a ferromagnetic phase above T_s=105-135 K, leading to magnetocaloric effects. The maximum value of ΔS_M was 1.19 J/(kg·K) at 100 K and 2.03 J/(kg·K) at 152 K for a magnetic field change of 5 T. Because both samples had large relative cooling power (RCP) and wide δT_FWHM, the study on systems with the (La_1-xHo_x)_2/3Ca_1/3MnO₃-related magnetic transitions may open an important field in searching good magnetic materials.     

Microstructure and microwave dielectric properties of Ba6-3xSm8+2xTi18O54 ceramics with various BaxSr1-xTiO3 additions

The Ba6-3xSm8+2xTi18O54 (x=2/3) microwave dielectric ceramics were prepared by traditional solid sate reaction technique. The ex-periment was based on the Ba6-3xSm8+2xTi18O54 (BST) microwave dielectric ceramics doped with a certain amount of Bi2O3, then the effects of BaxSr1-xTiO3 additives on the structure and microwave dielectric properties of Ba6-3xSm8+2xTi18O54 ceramics were investigated using X-ray diffraction and scanning electron microscopy. In this study, the small amount substitution of Sr for Ba was effective for the microwave dielec-tric properties of BST, especially the τf could be tuned to near zero. The result showed that the BST possessed excellent dielectric properties when the addition of Bi2O3 and BaxSr1-xTiO3 was 1 wt.% respectively: εr=79.6, Q?f=10789 GHz, τf=-1.5 ppm/oC.     

Impact of La3+ substitution on electrical,magnetic, dielectric and optical properties of Ni0.7Cu0.1Zn0.2LaxFe2–xO4 (0 < x < 0.035) system

The oxalate co-precipitation method was used to synthesize the La³⁺ substituted Ni–Cu–Zn (La–NCZ) nanoferrites having chemical composition Ni_0.7Cu_0.1Zn_0.2La_xFe_2–xO₄ (x = 0, 0.015, 0.025 and 0.035). DC resistivity study of nanoferrites shows both the conducting and semiconducting behaviour. The room temperature DC electrical resistivity of Ni–Cu–Zn (NCZ) nanoferrites decreases, whereas Curie temperature increases with increasing La³⁺ content. In the temperature range of 30–170 °C nanoferrites show p-type semiconducting behavior except x = 0.015; thereafter, they show n-type behaviour. The frequency dispersive initial permeability (μ_i) associated with its real and imaginary (μ′ and μ") parts are attributed to the domain wall movement and magnetic spin resonant. The μ_i, μ′ and μ" of La–NCZ nanoferrites are higher than those of pure NCZ nanoferrite. Dielectric constant (ε′), dielectric loss (ε″) and AC resistivity (ρ_AC) of La–NCZ nanoferrites show normal dielectric behaviour. It is found that ε′ of NCZ nanoferrites decreases with the increasing content of La³⁺ ions. The bandgap energy of La–NCZ nanoferrites is achieved in the range 1.36–1.70 eV confirming the semiconducting nature of materials.     

Tunable electronic band structure,luminescence properties and thermostability of(Gd_(1-x)La_x)_2Si_2O_7:Ce scintillator by adjusting La/Gd ratio

Mixed crystal strategy is an effective approach of improving the luminescence properties of optical materials and has been adopted widely in many systems.In this paper,the La-mixed Gd_2 Si_2 O_7:Ce polycrystalline samples were successfully synthesized by a sol-gel method.The crystal structure and luminescence properties were confirmed and discussed by XRD,UV-Vis luminescence spectra,and XEL,respectively.The vacuum ultraviolet excitation spectra and thermoluminescence glow curves were also systematically investigated and discussed at varied temperature.A combination of the first-principles calculations and optical characterization experiments was employed to study the electronic band structure of host material,revealing that the band gap is narrowed and the 5 d_1 level of Ce~(3+) shifts to higher energy as the La content increases.The luminescence the rmo-stability and activation energy were also measured and calculated.It indicates that thermo-stability is strongly dependent on the La concentration.An effective approach is developed to tune the electronic band structure,luminescence properties and thermostability of(Gd_(1-x)La_x)_2 Si_2 O_7:Ce scintillator by adjusting La/Gd ratio.