Effects of Sm3+ Substitution on Dielectric Properties of Ca1−xSm2x/3TiO3 Ceramics at Microwave Frequencies

Microwave dielectric properties of Ca_{1- x} Sm_{2 x /3}TiO₃ ceramics were investigated as a function of the amount of Sm³⁺ substitution (0.0 ≤ x ≤ 0.8). The structure was changed from orthorhombic perovskite at x = 0.0 to tetragonal at x = 0.6. As the calcium vacancy concentration increased with increased Sm³⁺ substitution, the unloaded Q value (similar/congruent 1/tan delta) increased up to the solid-solution limit at x = 0.6 and then decreased because of formation of the secondary phase Sm₂Ti₂O₇. The dielectric constant decreased with increased Sm³⁺ substitution. The effects of Sm³⁺ substitution on dielectric loss and dielectric constant of the specimens were analyzed by the infrared reflectivity spectra in the range 50–4000 cm⁻¹, which were evaluated using the Kramers-Kronig analysis and classical oscillator model. The correlations among dielectric constant, dielectric loss, and dispersion parameters were studied.     

Microwave Dielectric Properties of CaTiO3-CaAl1/2Nb1/2O3 Ceramics Doped with Li3NbO4

The microwave dielectric properties of CaTi_{1− x} (Al_1/2Nb_1/2) _x O₃ solid solutions (0.3 ≤ x ≤ 0.7) have been investigated. The sintered samples had perovskite structures similar to CaTiO₃. The substitution of Ti⁴⁺ by Al³⁺/Nb⁵⁺ improved the quality factor Q of the sintered specimens. A small addition of Li₃NbO₄ (about 1 wt%) was found to be very effective for lowering sintering temperature of ceramics from 1450–1500° to 1300°C. The composition with x = 0.5 sintered at 1300°C for 5 h revealed excellent dielectric properties, namely, a dielectric constant (ɛ_r) of 48, a Q × f value of 32 100 GHz, and a temperature coefficient of the resonant frequency (τ_f) of −2 ppm/K. Li₃NbO₄ as a sintering additive had no harmful influence on τ_f of ceramics.     

Effect of V2O5 Doping on the Sintering and Dielectric Properties of M-Phase Li1+x−yNb1−x−3yTix+4yO3 Ceramics

The effect of the addition of V₂O₅ on the structure, sintering and dielectric properties of M -phase (Li_{1+ x − y} Nb_{1− x −3 y} Ti _x +4 _y )O₃ ceramics has been investigated. Homogeneous substitution of V⁵⁺ for Nb⁵⁺ was obtained in LiNb_{0.6(1− x )}V_{0.6 x} Ti_0.5O₃ for x ≤ 0.02. The addition of V₂O₅ led to a large reduction in the sintering temperature and samples with x = 0.02 could be fully densified at 900°C. The substitution of vanadia had a relatively minor adverse effect on the microwave dielectric properties of the M -phase system and the x = 0.02 ceramics had [alt epsilon]_r= 66, Q × f = 3800 at 5.6 GHz, and τ_f= 11 ppm/°C. Preliminary investigations suggest that silver metallization does not diffuse into the V₂O₅-doped M -phase ceramics at 900°C, making these materials potential candidates for low-temperature cofired ceramic (LTCC) applications.     

Microwave Dielectric Properties of CaTiO3-Ca(Al1/2Ta1/2)O3 Ceramics

The microwave dielectric properties of CaTi_1-χ(Al_1/2Ta_1/2)_cHO₃ solid solutions (0.3 ≤χ≤ 0.5) have been investigated. The ceramic samples had perovskite structures similar to CaTiO₃. The partial substitution of Ti₄₊ by a coupled Al₃₊/Ta_s+ permitted improvement of the quality factor Q . The dielectric constant (τ_r) and temperature coefficient of resonant frequency (τ_r) decrease rapidly with an increase of χ. A new high-quality microwave dielectric material was found at χ= 0.46 with σ_r= 46.5, Q f = 27300 GHz, and π_f= 0 ppm/°C. The relationship between microstructures and dielectric properties is presented.     

Phase Relations in the Na0.5Bi0.5TiO3–Li3xLa(2/3)−x□(1/3)−2xTiO3 System

The phase relations and the mechanism of solid-state synthesis for the Na_0.5Bi_0.5TiO₃–Li_{3 x} La_{(2/3)− x} □_{(1/3)−2 x} TiO₃ system were investigated using X-ray powder diffraction, scanning electron microscopy, and thermal analysis. The study revealed that the extent of the homogeneity range—which is related to the A-site substitution between (Na_0.5Bi_0.5)²⁺ and (Li_{3 x} La_{(2/3)− x} □_{(1/3)−2 x} )²⁺ pseudo cations of a perovskite structure—depends strongly on the ordering of the (Li_{3 x} La_{(2/3)− x} □_{(1/3)−2 x} )²⁺ species. The solid-state reaction of the compounds in the homogeneity range is completed only after multiple high-temperature firings. However, the system is also subjected to a slow thermal decomposition; this is particularly so for the compounds with a high × value and an increased Li_{3 x} La_{(2/3)− x} □_{(1/3)−2 x} TiO₃ concentration.     

Formation of Sm2+ lons in Sol-Gel-Derived Glasses of the System Na2 O-Al2O3-SiO2

Samarium ions (Sm²⁺) incorporated into aluminosilicate glasses by a sol-gel process showed persistent spectral hole burning at room temperature. Gels of the system Na₂O-Al₂O₃SiO₂ synthesized by the hydrolysis of Si(OC₂H₅)₄, Al(OC₄H₉)₃, CH₃ COONa, and SmCl₃·6H₂O were heated in air at 500°C, then reacted with H₂ gas to form Sm²⁺ ions. Whereas Al³⁺ ions effectively dispersed the Sm³⁺ ions in the glass structure, Na⁺ ions were not effective. The Al₂O₃-SiO₂ glasses proved appropriate for reacting the Sm³⁺ ions with H₂ gas and exhibited the intense photoluminescence of Sm²⁺ ions. The reaction of Sm³⁺ ions with H₂ in the Al₂O₂-SiO₂ glasses was determined by first-order kinetics, and the activation energy equaled 95 kJ/mol. At 800°C, the maximum photoluminescence of the Sm²⁺ ions was achieved within 20 min.     

Microwave Dielectric Properties of (1−x)(Na1/2Nd1/2)TiO3−xLa(Mg1/2Ti1/2)O3 via Ordering and Far IR Reflectivity Spectra

Microwave dielectric properties of (1− x )(Na_1/2Nd_1/2)TiO₃(NNT)− x La(Mg_1/2Ti_1/2)O₃(LMT) system have been investigated with focus on structural ordering and far IR reflectivity spectra. A single perovskite phase was found to exist with various superlattice reflections over the entire compositional range. 1:1 ordering observed in the (111) reflection of X-ray diffraction patterns was found to progress significantly in the specimens above x =0.8. The ordering characteristics that presumably related to B-site Mg/Ti ordering were assumed to affect favorably the quality factor at microwave frequencies. The increase of the quality factor also could be explained in terms of the decrease of lattice anharmonicity with LMT by analysis of far IR reflectivity spectra. As expected from the values of pure NNT and LMT, the dielectric constant and the temperature coefficient of frequency tended to gradually decrease with increasing LMT content.     

X-ray Diffraction and 151Eu Mössbauer Spectroscopic Study of the Hf1−xEuxO2−x/2(0 ≤x≤ 1.0) System

Powder X-ray diffractometry (XRD) and ¹⁵¹Eu Mössbauer spectroscopy were performed for samples prepared in the temperature range 1500–1500°C for the hafnia–europia (HfO₂–Eu₂O₃) system Eu _x Hf_{1− x} O_{2− x /2}(0 ≤ x ≤ 1.0). The XRD results showed that two types of solid solution phases formed in the composition range 0.25 ≤ x ≤ 0.725: an ordered pyrochlore-type phase in the middle-composition range (0.45 < x < 0.575) and a disordered fluorite-type phase, enveloping the pyrochlore-type phase on both sides, in the composition ranges 0.25 ≤ x ≤ 0.40 and 0.60 ≤ x ≤ 0.725. ¹⁵¹Eu Mössbauer spectroscopy sensitively probes local environmental changes around trivalent europium (Eu³⁺) caused by the formation of these solid solution phases. In addition to the broad, single Mössbauer spectra observed in this study for the Eu³⁺, the values of isomer shift (IS) exhibited a pronounced minimum in the neighborhood of the stoichiometric pyrochlore phase ( x ≈ 0.5). Such IS behavior of Eu³⁺ was interpreted based on the XRD crystallographic information that the ordered pyrochlore phase has a longer (in fact, the longest) average Eu–O bond length than those of the disordered fluorite phases on both sides or the monoclinic (and C-type) Eu₂O₃at x = 1.0.     

Enhancement of Giant Dielectric Response in CaCu3Ti4O12 Ceramics by Zn Substitution

Zn-substituted CaCu₃Ti₄O₁₂ ceramics were synthesized by solid-state sintering. Their microstructures and dielectric properties were investigated. Ca(Cu_{1− x} Zn _x )₃Ti₄O₁₂ single-phase structures were obtained up to x =0.1, and the Cu⁺/Cu²⁺ and Ti³⁺/Ti⁴⁺ mixed-valent structure was enhanced with increasing Zn substitution. The giant dielectric response was significantly enhanced by Zn substitution. The dielectric constant increased with increasing x , and a giant dielectric constant plateau as high as ∼9 × 10⁴ was achieved for x =0.1 at 10 kHz, while that for x =0 was ∼3 × 10⁴. The enhanced giant dielectric response was profoundly concerned with the modified mixed-valent structure.     

Structure and Dielectric Properties of Pb(Sc2/3W1/3)O3–Pb(Zr/Ti)O3 Relaxors

The structure and dielectric properties of (1− x )Pb(Sc_2/3W_1/3)O₃–( x )Pb(Zr/Ti)O₃ ceramics have been investigated over a full substitution range. All compositions with x < 0.5 adopt a cubic perovskite structure; however, for x ≤ 0.25 a doubled cell results from a 1:1 ordered distribution of the B-site cations. The structural order in Pb(Sc_2/3W_1/3)O₃ (PSW) can be described by a random-site model with one cation site occupied by Sc³⁺ and the other by a random distribution of (Sc_1/3³⁺W_2/3⁶⁺). The ordering is destabilized in solid solutions of PSW with PbZrO₃ (PSW–PZ), but stabilized by PbTiO₃ in the (1− x )PSW–( x )PT system. The changes in order are accompanied by alterations in the dielectric response of the two systems. For PSW–PZ the temperature of the permittivity maximum ( T _ɛ,max) increases linearly with x ; however, for PSW–PT T _ɛ,max decreases in the ordered region (up to x = 0.25) and then increases rapidly as the order is lost. Similar effects were produced by modifying the degree of order of (0.75)PSW–(0.25)PT; when the order parameter was reduced from ∼1.0 to ∼0.65, T _ɛ,max increased by more than 60°C.     

Crossover of Ba(Ti,Y)O3 Solid Solutions to Ba3Ti2YO8.5–BaTiO3 Composites and their Dielectric Properties

Ceramic samples with the nominal composition (1− x ) BaTiO₃+ x Ba₃Ti₂YO_8.5 ( x =0−0.535) were prepared by the mixed oxide method. X-ray diffraction (XRD) analysis shows that the materials are of single phase with a cubic symmetry as x ≤0.16. The compositions of the solid solutions ( x ≤0.16) can be expressed equivalently as Ba(Ti_{1− y} Y _y )O_3−δ ( y ≤0.122, y = x /(1+2 x )). For x >0.16, the materials are diphasic composites consisting of Ba(Ti_{1− y} Y _y )O₃ ( y =0.122) and Ba₃Ti₂YO_8.5. The microstructure observation by scanning electron microscopy supports the XRD result. The dielectric behavior and phase transitions of the solid solutions ( x ≤0.16) vary with different Y concentrations. The dielectric constant of the composites ( x >0.16) follows approximately the Lichteneker relation in a wide temperature range.     

Peculiar Dielectric Behaviors of (Na1/2Bi1/2)0.87Pb0.13TiO3 Thin Films

PbTiO₃-doped sodium bismuth titanate (Na_1/2Bi_1/2)_{1− x} Pb _x TiO₃ of perovskite structure is one of the best-known piezoelectrics/ferroelectrics. However, it has not been properly investigated in any thin-film forms. In this study, the dielectric properties of (Na_1/2Bi_1/2)_0.87Pb_0.13TiO₃ thin films synthesized via a sol–gel route were investigated. They exhibit a strong frequency dispersion of the dielectric permittivity at relatively high frequencies, which is shifted to lower frequencies with increasing temperature. The electrical behavior can be fitted using Jonscher's universal law for dielectric relaxation. The peculiar dielectric behaviors observed can be ascribed to the coexistence of two different dielectric phases in the films, which is believed to be associated with the growth of the local Pb²⁺TiO₃ nanoclusters upon substitution of Pb²⁺ for Na⁺/Bi³⁺ in the (Na_1/2Bi_1/2)_{1− x} Pb _x TiO₃ films.     

Structure and Microwave Dielectric Properties of (Zn1−xCox)TiO3 Ceramics

Dielectric ceramics in the system (Zn_{1− x} Co _x )TiO₃ ( x = 0–1) were synthesized by the solid-state reaction route. The phase distribution, microstructure, and dielectric properties were characterized by using powder X-ray diffraction analysis, electron microscopy, and microwave measurement techniques. Three phase composition regions were identified in the specimens sintered at 1150°C; [spinel + rutile] at 0 ≤ x ≤ 0.5, [spinel + ilmenite + rutile] at 0.5 < x ≤ 0.7, and [ilmenite] phase at 0.7 < x ≤ 1. For the 0 ≤ x ≤ 0.5 region, the amount of Ti-rich precipitates incorporated into the spinel phase decreased with the Co content at 0 ≤ x ≤ 0.5, with a concomitant increase of the rutile phase. The ilmenite phase appeared for high Co content. The microwave dielectric properties depended on the phase composition and volume according to the three phase regions, where the relative amount of rutile to the spinel or ilmenite determined the dielectric properties. The dielectric constant as a function of Co addition was modeled with a Maxwell mixing rule. An optimum phase distribution was determined in this system with dielectric constant of 25, a Q * f 70 000 GHz, and a low temperature coefficient of the resonant frequency.     

Tin Substitution for Titanium in Ba6−3xNd8+2xTi18O54 Microwave Dielectric Ceramics

Tin (Sn) substitution for titanium (Ti) was investigated in Ba_{6−3 x} Nd_{8+2 x} Ti₁₈O₅₄ ( x =1/2, 2/3, and 3/4) ceramics. A small amount ( z <0.1) of Sn substitution resulted in Ba_{6−3 x} Nd_{8+2 x} (Ti_{1− z} Sn _z )₁₈O₅₄ solid solutions, and some secondary phases were observed with increasing Sn content. A small amount of Sn substitution improved the Q f value significantly, while, due to the formation of secondary phases, the Q f value degraded sharply for larger Sn content. The relative dielectric constant (ɛ_r) decreased with increasing Sn-content, while the temperature coefficient of resonant frequency (τ_f) generally decreased, although an obvious fluctuation was observed for x =3/4.     

Ordered Structure and Dielectric Properties of Lanthanum-Substituted Ba(Mg1/3Ta2/3)O3

Both 1:2 and 1:1 ordered structures form in the perovskite solid solutions of La-substituted BMT Ba_{1− x} La _x (Mg_{(1+ x )/3}Ta_{(2− x )/3})O₃, sintered at 1600°C. The 1:2 ordered structure exists in the composition range 0.0 ≤ x ≤ 0.12, while that of 1:1 ordered structure exists in a wider composition range 0.04 ≤ x ≤ 1.0. Two ordered phases coexist in 0.04 ≤ x ≤ 0.12. High-resolution micrographs indicate that 1:2 and 1:1 ordered domains coexist in one grain. The ordering parameter of 1:2 phase decreases with x , yet that of 1:1 phase increases with x . Both increase with soak time. Variations in ordering are discussed in terms of cation occupancy and crystal chemistry. The quality factor increases with x , reaches a maximum, then decreases with x . The dielectric constant increases with x first, and levels off.     

Microstructure and Microwave Dielectric Properties of (1−x)Ca(Mg1/3Ta2/3)O3/xCaTiO3 Ceramics

Dense (1− x )Ca(Mg_1/3Ta_2/3)O₃/ x CaTiO₃ ceramics (0.1≤ x ≤0.9) were prepared by a solid-state reaction process. The crystal structures and microstructures were characterized by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. Single-phase solid solutions were obtained in the entire composition range. Long-range 1:2 ordering of B-site cations and oxygen octahedra tilting lead to the monoclinic symmetry with space group P 2₁/ c for x =0.1. For x above 0.1, the long-range ordering was destroyed and the crystal structure became the orthorhombic with space group Pbnm . The microwave dielectric properties showed a strong dependence on the composition and microstructure. The dielectric constant and temperature coefficient of resonant frequency increased nonlinearly as the CaTiO₃ content increased while the Qf values decreased approximately linearly. Good combination of microwave dielectric properties was obtained at x =0.45, where ɛ_r=45.1, Qf =34 800 GHz, and τ_f=17.4 ppm/°C.     

Structure-Property Phase Diagram of BaZrxTi1−xO3 System

In the course of searching environmental friendly lead-free relaxor ferroelectrics a complete phase diagram of barium zirconate titanate, Ba(Zr _x Ti_{1− x} )O₃ system with compositions 0.00≤ x ≤1.00 has been developed based on their dielectric behavior. It has been shown that BaZr _x Ti_{1− x} O₃ system depending on the composition, successively depicts the properties extending from simple dielectric (pure BaZrO₃) to polar cluster dielectric, relaxor ferroelectric, second order like diffuse phase transition, ferroelectric with pinched phase transitions and then to a proper ferroelectric (pure BaTiO₃). A comprehensive structure–property correlation of BaZr _x Ti_{1− x} O₃ ceramics has been studied to understand the various ferroelectric phenomena in the whole phase diagram.     

Synthesis and Characterization of (Zn,Cd)TiO3 by a Modified Sol–Gel Method

Ilmenite-type (Zn_{1− x} Cd _x )TiO₃ (0≤ x ≤0.15 and 0.8≤ x ≤1.0) was synthesized by a modified sol–gel route including the Pechini process via two-step heat treatments. The thermal stability of (Zn_{1− x} Cd _x )TiO₃ depended on the amount of cadmium content. The as-synthesized (Zn_{1− x} Cd _x )TiO₃ (0≤ x ≤0.15 and 0.8≤ x ≤1.0) showed higher thermal stability than that of ZnTiO₃. The variation of the dielectric constant of all synthesized (Zn_{1− x} Cd _x )TiO₃ samples for all measurement frequencies showed a similar tendency. The dielectric constant of each (Zn_{1− x} Cd _x )TiO₃ sample decreased first with increasing frequencies and then increased slightly when the frequency was up to 10⁷ Hz. Moreover, the dielectric loss tangent of all synthesized (Zn_{1− x} Cd _x )TiO₃ samples for all measurement frequencies also changed in similar patterns. The dielectric loss tangent decreased with increasing measurement frequencies. The microwave dielectric properties of (Zn_{1− x} Cd _x )TiO₃ were changed with the cadmium doping content in the range of microwave frequency.     

A- and B Site Cosubstituted Ba6−3xSm8+2xTi18O54Microwave Dielectric Ceramics

Tin (Sn) substitution into the B-site and Nd/Sn cosubstitution into the A- and B-sites were investigated in a Ba _{6−3 x} Sm_{8+2 x} Ti₁₈O₅₄solid solution ( x = 2/3). A small amount of tin substitution for titanium improved the temperature coefficient of resonant frequency (τ_f) but led to a decrease of the relative dielectric constant (ɛ) and the quality factor ( Qf ). The Ba_{6−3 x} Sm_{8+2 x} (Ti_{1− z} Sn_z)₁₈O₅₄-based tungsten-bronze phase became unstable for compositions with a tin content of ≥10 mol%, where BaSm₂O₄and Sm₂(Sn,Ti)₂O₇appeared, and finally, these phases became the major phases. On the other hand, Nd/Sn cosubstitution led to a good combination of high ɛ, high Qf , and near-zero τ_f. Excellent microwave dielectric properties were achieved in Ba_{6−3 x} (Sm_{1− y} Nd _y )_{8+2 x} (Ti_{1− z} Sn _z )₁₈O₅₄ceramics with y = 0.8 and z = 0.05 sintered at 1360°C for 3 h: ɛ= 82, Qf = 10 000 GHz, and calculated τ_f=+17 ppm/°C. The tolerance factor and electronegativity difference exhibited important effects on the microwave dielectric properties, especially the Qf value. A large tolerance factor and high electronegativity difference generally led to a higher Qf value.     

Ferroelectric and Piezoelectric Properties of Na1−xBaxNb1−xTixO3 Ceramics

Piezoelectric ceramics Na_{1− x} Ba _x Nb_{1− x} Ti _x O₃ with low BaTiO₃ concentrations x have been prepared by the solid-state reaction method, and their ferroelectric and piezoelectric properties have been studied. The ceramics are classic ferroelectrics when x ≤0.10, and the ferroelectric–paraelectric phase transition becomes diffusive when x ≥0.15. A low doping level of BaTiO₃ changes the NaNbO₃ ceramics from antiferroelectric to ferroelectric. With the increase in BaTiO₃ doping level, the Curie temperature of ceramics decreases linearly and the remnant polarization and coercive field also decrease, while their dielectric constant increases. Na_0.9Ba_0.1Nb_0.9Ti_0.1O₃ ceramics show the largest piezoelectric constant d ₃₃ (147 pC/N) and good sinterability, suggesting that it is a good candidate for lead-free piezoelectric ceramics.