Structure characteristics and microwave dielectric properties of Pr_(2)(Zr_(1-x)Ti_(x))_(3)(MoO_(4))_(9) solid solution ceramic with a stable temperature coefficient

Pr_(2)(Zr_(1−x)Ti_(x))_(3)(MoO_(4))_(9)(x=0.1-1.0)ceramics were prepared via a conventional solid-state method,the dependence of crystal structure and bond characteristics on microwave dielectric properties was investigated systemically.The X-ray diffraction patterns indicated that the single-phase Pr_(2)Zr_(3)(MoO_(4))_(9)structure was formed in all the specimens.As the Ti^(4+)content increased,the lattice volume gradually decreased,which was ascribed to the fact that the ionic radius of Ti^(4+)was smaller than that of Zr^(4+).Notably,outstanding microwave dielectric properties withεr of 10.73-16.35,Q·f values of 80,696-18,726 GHz and minorτ_(f) values−14.1-−2.6 ppm/℃were achieved in Pr_(2)(Zr_(1−x)Ti_(x))_(3)(MoO_(4))_(9)ceramics.Theε_(r) increased with the rising x values,which was associated with the increase ofα/Vm values.The decreasing Q·f was affected by the decline of lattice energy of[Zr/TiO_(6)]octahedral.Theτf value was dominated by[Zr/TiO_(6)]octahedral distortion,Mo-O bond energy,bond strength and B-site bond valence.Furthermore,infrared reflection spectra suggested that the properties were mainly caused by the absorption of phonon,and the dielectric loss could be further reduced by optimizing the experimental process.

Crystal structure,chemical bond characteristics,infrared reflection spectrum,and microwave dielectric properties of Nd_(2)(Zr_(1−x)Ti_(x))_(3)(MoO_(4))_(9) ceramics

Microwave dielectric ceramics(MWDCs)with low dielectric constant and low dielectric loss are desired in contemporary society,where the communication frequency is developing to high frequency(sub-6G).Herein,Nd_(2)(Zr_(1−x)Ti_(x))_(3)(MoO_(4))_(9)(NZ_(1−x)T_(x)M,x=0.02-0.10)ceramics were prepared through a solid-phase process.According to X-ray diffraction(XRD)patterns,the ceramics could form a pure crystal structure with the R3c(167)space group.The internal parameters affecting the properties of the ceramics were calculated and analyzed by employing Clausius-Mossotti relationship,Shannon’s rule,and Phillips-van Vechten-Levine(P-V-L)theory.Furthermore,theoretical dielectric loss of the ceramics was measured and analyzed by a Fourier transform infrared(IR)radiation spectrometer.Notably,when x=0.08 and sintered at 700℃,optimal microwave dielectric properties of the ceramics were obtained,including a dielectric constant(ε_(r))=10.94,Q·f=82,525 GHz(at 9.62 GHz),and near-zero resonant frequency temperature coefficient(τ_(f))=−12.99 ppm/℃.This study not only obtained an MWDC with excellent properties but also deeply analyzed the effects of Ti^(4+)on the microwave dielectric properties and chemical bond characteristics of Nd_(2)Zr_(3)(MoO_(4))_(9)(NZM),which laid a solid foundation for the development of rare-earth molybdate MWDC system.

Structure,defects,and microwave dielectric properties of Al-doped and Al/Nd co-doped Ba_(4)Nd_(9.33)Ti_(18)O_(54)ceramics

Low-loss tungsten–bronze microwave dielectric ceramics are dielectric materials with potential application value for miniaturized dielectric filters and antennas in the fifth-generation(5G)communication technology.In this work,a novel Al/Nd co-doping method of Ba_(4)Nd_(9.33)Ti_(18)O_(54)(BNT)ceramics with a chemical formula of Ba_(4)Nd_(9.33+z/3)Ti_(18−z)Al_(z)O_(54)(BNT–AN,0≤z≤2)was proposed to improve the dielectric properties through structural and defect modulation.Together with Al-doped ceramics(Ba_(4)Nd_(9.33)Ti_(18−z)Al_(4z/3)O_(54),BNT–A,0≤z≤2)for comparison,the ceramics were prepared by a solid state method.It is found that Al/Nd co-doping method has a significant effect on improving the dielectric properties compared with Al doping.As the doping amount z increased,the relative dielectric constant(εr)and the temperature coefficient of resonant frequency(τf)of the ceramics decreased,and the Q×f values of the ceramics obviously increased when z≤1.5.Excellent microwave dielectric properties ofεr=72.2,Q×f=16,480 GHz,andτf=+14.3 ppm/℃were achieved in BNT–AN ceramics with z=1.25.Raman spectroscopy and thermally stimulated depolarization current(TSDC)technique were firstly combined to analyze the structures and defects in microwave dielectric ceramics.It is shown that the improvement on Q×f values was originated from the decrease in the strength of the A-site cation vibration and the concentration of oxygen vacancies(VO××),demonstrating the effect and mechanism underlying for structural and defect modulation on the performance improvement of microwave dielectric ceramics.

Thermally stable polymer-ceramic composites for microwave antenna applications

Polymer-ceramic composites were prepared by twin screw melt extrusion with high-density polyethylene (HDPE) as the matrix and polystyrene-coated BaO-Nd2O3-TiO2 (BNT) ceramics as the filling material.Interestingly,the incorporation of polystyrene (PS) by the coating route could significantly improve the thermal behaviors of the composites (HDPE-PS/BNT),besides the temperature stability of dielectric properties and thermal displacement.The microwave dielectric properties of the composites were investigated systematically.The results indicated that,as the volume fraction of BNT ceramic particles increased from 10 to 50 vol％ in the composites,the dielectric constant increased from 3.54 (9.23 GHz) to 13.14 (7.20 GHz),which can be beneficial for the miniaturization of microwave devices;the dielectric loss tangent was relatively low (0.0003-0.0012);more importantly,the ratio of PS to HDPE increased accordingly,making the composite containing 50 vol％ BNT ceramics have a low value of temperature coefficient of resonant frequency (τf =-11.2 ppm/℃) from-20 to 60 ℃.The GPS microstrip antennas were therefore designed and prepared from the HDPE-PS/BNT composites.They possessed good thermal stability (τf=23.6 ppm/℃) over a temperature range of-20 to 60 ℃,promising to meet the requirements of practical antenna applications.

Large electrostrictive effect and strong photoluminescence properties in Sm_(2)O_(3)-modified lead-free potassium sodium niobate-based piezoelectric ceramics

In this work,the phase transition behavior and electrostrictive and photoluminescence properties of Sm_(2)O_(3)-modified 0.965(K_(0.48)Na_(0.52))(Nb_(0.95)Sb_(0.05))e_(0.035)Bi_(0.5)(Na_(0.82)K_(0.18))_(0.5)HfO_(3)(KNNSe0.035BNKH)ceramics were investigated.Results showed that the phase structure of the Sm2O3-modified ceramics evolved from coexisting orthogonal and tetragonal ferroelectric phases to a relaxor pseudocubic phase along with the strong destruction of the long-range ferroelectric order.Domain switching in Smmodified ceramics with a relaxor pseudocubic phase became difficult,evident from the PFM images.Consequently,large electrostrictive effect with an electrostrictive coefficient of 0.022 m4/C2 was obtained in 1.0 mol%Sm-modified samples.With regard to long-term stability,the materials exhibited temperature-independent(20-100℃)and fatiguefree(up to 105 cycles)behavior,which guarantees their application in various devices.The KNNSe0.035BNKHexSm ceramics have the advantages of photoluminescence performance with bright orange emission under 407 nm visible light excitation.Overall,KNNS0.035BNKHxSm ceramics have broad application prospects in multifunction devices due to their large electrostrictive effect,excellent photoluminescence performance,and long-term stability.

Lattice vibrational characteristics,crystal structures and dielectric properties of non-stoichiometric Nd_((1+x))(Mg_(1/2)Sn_(1/2))O_(3) ceramics

Non-stoichiometric Nd_((1+x))(Mg_(1/2)Sn_(1/2))O_(3)(-0.04=x≤0.04,NMS)ceramics were fabricated via a conventional solid-state reaction method.Crystal structures and morphologies were investigated by Xray diffraction(XRD)and scanning electron microscopy(SEM),respectively.The main crystalline phase is monoclinic Nd(Mg_(1/2)Sn_(1/2))O_(3) with a double perovskite structure(P21/n space group)for the NMS system proved by XRD.The sample at x=0.01 has the best crystallinity and evenly distributed crystal grains observed by SEM.The optimum performances(ε_(r)=19.87,Q×f=41840 GHz,f=12.05 GHz)are obtained at x=0.01.Lattice vibrational modes of the Raman spectra were assigned and illustrated,in detail.The dielectric properties obtained by fitting infrared reflectance spectra with the help of four-parameter semi-quantum model are consistent with the calculated values by microscopic polarization and damping coefficients.The reverse translational vibration of the NdeMgO_(6),the F_(5u)^((5)) mode,provides the greatest contribution to the dielectric response.The relationships between crystal structures and dielectric properties were mainly established using lattice vibrational modes as a media.

Sintering characteristics, crystal structure and dielectric properties of cobalt-tungsten doped molybdate-based ceramics at microwave frequency

In this study,a sequence of Ce_(2)[Zr_(1-x)(Co_(1/2)W_(1/2))_(x)]_(3)(MoO_(4))_(9)(CZ_(1-x)(CW)_(x)M)(x=0.02e0.10)ceramics with excellent microwave dielectric properties were obtained by the traditional solid-phase method.The crystal structure,dielectric properties,and chemical bond characters of the ceramics were characterized and analyzed.X-ray diffraction and Rietveld refinement analysis show that CZ_(1-x)(CW)_(x)M could form a single-phase of the triangular crystal system in the entire doping range.The microstructure of the ceramic samples was obtained by scanning electron microscopy.The sintering temperature was reduced and the gain of the sample was refined as the increase of doping ion content.Furthermore,the intrinsic factors affecting the properties of CZ_(1-x)(CW)_(x)M were analyzed by employing P-V-L theory and through in-depth infrared analysis.When x was 0.04 and the sintering temperature was 750C,the best dielectric properties of the samples were achieved,includingεr=9.95,Q·f=80,803 GHz(at 9.99 GHz),and tf=-9.10 ppm/℃.