Structure and electrical properties of MnO doped (Ba<Subscript>0.96</Subscript>Ca<Subscript>0.04</Subscript>)(Ti<Subscript>0.92</Subscript>Sn<Subscript>0.08</Subscript>)O<Subscript>3</Subscript> lead free ceramics

In this work, (Ba_0.96Ca_0.04)(Ti_0.92Sn_0.08)O₃–xmol MnO (BCTS–xMn) lead-free piezoelectric ceramics were fabricated by the conventional solid-state technique. The composition dependence (0 ≤ x ≤ 3.0 %) of the microstructure, phase structure, and electrical properties was systematically investigated. An O–T phase structure was obtained in all ceramics, and the sintering behavior of the BCTS ceramics was gradually improved by doping MnO content. In addition, the relationship between poling temperature and piezoelectric activity was discussed. The ceramics with x = 1.5 % sintering at temperature of 1330 °C demonstrated an optimum electrical behavior: d ₃₃ ~ 475 pC/N, k _p ~ 50 %, ε _r ~ 4060, tanδ ~ 0.4 %, P _r ~ 10.3 μC/cm², E _c ~ 1.35 kV/mm, T _C ~ 82 °C, strain ~0.114 % and \(d_{33}^{*}\) ~ 525 pm/V. As a result, we achieved a preferable electric performance in BaTiO₃-based ceramics with lower sintering temperature, suggesting that the BCTS–xMn material system is a promising candidate for lead-free piezoelectric ceramics.     

Strong up-conversion luminescence and electrical properties of SrBi<Subscript>4</Subscript>Ti<Subscript>4</Subscript>O<Subscript>15</Subscript> multifunctional ceramics by Er<Superscript>3+</Superscript> doping

Novel green-emitting piezoelectric ceramics of SrBi_4?x Er _x Ti₄O₁₅ (SBT-xEr) were prepared. Strong up-conversion with bright green (524 and 548 nm) and a relatively weak red (660 nm) emission bands were obtained under 980 nm excitation at room temperature, which is attributed to the intra 4f–4f electronic transition of (²H_11/2, ⁴S_3/2)–⁴I_15/2 and the transition from ⁴F_9/2 to ⁴I_15/2 of Er³⁺ ions, respectively. Simultaneously, Er³⁺ doping promotes the electrical properties. At 0.8 mol%Er, the optimal electric properties with high Curie temperature of T _c?~527?°C, large remanent polarization of 2P _r?~14.92 μC/cm² and piezoelectric constant of d ₃₃?~17 pC/N was achieved. As a multifunctional material, Er³⁺ doped SBT showed a great potential to be used in 3D-display, bio-imaging, solid state laser and optical temperature sensor.     

Synthesis of anisotropic NaNbO<Subscript>3</Subscript> seed crystals and fabrication of textured (K<Subscript>0.5</Subscript>Na<Subscript>0.5</Subscript>)NbO<Subscript>3</Subscript>-based ceramics

High aspect ratio patelike NaNbO₃ particles with pure perovskite structure have been successfully synthesized by topochemical microcrystal conversion (TMC) from plate-like precursor particles of the layer-structured Bi_2.5Na_3.5Nb₅O₁₈. By changing the Bi_2.5Na_3.5Nb₅O₁₈/Na₂CO₃ ratio, large and thin NaNbO₃ particles with a thickness of approximately 0.5 μm and a width of approximately 20 μm were obtained. The obtained NaNbO₃ particles is quite suitable for fabricating textured (K_0.5Na_0.5)NbO₃-based ceramics. Using the fine platelike NaNbO₃ particles as templates, dense <001> -oriented (K_0.5Na_0.5)NbO₃-0.5 mol %MnO₂ ceramics with high texture quality (Lotgering factor F ₀₀₁ = 87 %) and excellent piezoelectric properties were produced by templated grain growth. Compared with randomly oriented ceramics, textured samples show greatly enhanced properties. The room-temperature strain S, the piezoelectric coefficient d ₃₃ ^* and d ₃₃ reach up to 0.093 %, 233 pm/V and 195pC/N, respectively, which are all about 1.5 times larger than those of non-textured ceramics.     

Effects of Ge<Superscript>4+</Superscript> acceptor dopant on sintering and electrical properties of (K<Subscript>0.5</Subscript>Na<Subscript>0.5</Subscript>)NbO<Subscript>3</Subscript> lead-free piezoceramics

Lead-free (K_0.5Na_0.5)(Nb_1-xGe _x )O₃ (KNN-xGe, where x = 0-0.01) piezoelectric ceramics were prepared by conventional ceramic processing. The effects of Ge⁴⁺ cation doping on the phase compositions, microstructure and electrical properties of KNN ceramics were studied. SEM images show that Ge⁴⁺ cation doping improved the sintering and promoted the grain growth of the KNN ceramics. Dielectric and ferroelectric measurements proved that Ge⁴⁺ cations substituted Nb⁵⁺ ions as acceptors, and the Curie temperature (T_C) shows an almost linear decrease with increasing the Ge⁴⁺ content. Combining this result with microstructure observations and electrical measurements, it is concluded that the optimal sintering temperature for KNN-xGe ceramics was 1020°C. Ge⁴⁺ doping less than 0.4 mol.%can improve the compositional homogeneity and piezoelectric properties of KNN ceramics. The KNN-xGe ceramics with x = 0.2% exhibited the best piezoelectric properties: piezoelectric constant d₃₃ = 120 pC/N, planar electromechanical coupling coefficient k_p = 34.7%, mechanical quality factor Q_m = 130, and tanδ = 3.6%.     

Very high thermal stability with excellent dielectric,and non-ohmics properties of Mg-doped CaCu<Subscript>3</Subscript>Ti<Subscript>4.2</Subscript>O<Subscript>12</Subscript> ceramics

In this work, the nominal CaCu_3?xMg_xTi_4.2O₁₂ (0.00, 0.05 and 0.10) ceramics were prepared by sintering pellets of their precursor powders obtained by a polymer pyrolysis solution method at 1100 °C for different sintering time of 8 and 12 h. Very low loss tangent (tanδ)?<?0.009–0.014 and giant dielectric constant (ε′) ～?1.1?×?10⁴–1.8?×?10⁴ with excellent temperature coefficient (Δε′) less than ±?15% in a temperature range of ??60 to 210 °C were achieved. These excellent performances suggested a potent application of the ceramics for high temperature X8R and X9R capacitors. It was found that tanδ values decreased with increasing Mg²⁺ dopants due to the increase of grain boundary resistance (R_gb) caused by the very high density of grain, resulting from the substitution of small ionic radius Mg²⁺ dopants in the structure. In addition, CaCu_3?xMg_xTi_4.2O₁₂ ceramics displayed non-linear characteristics with the significant enhancements of a non-linear coefficient (α) and a breakdown field (E_b) due to Mg²⁺doping. The high values of ε′ (14012), α (13.64) and E_b (5977.02 V/cm) with very low tanδ value (0.009) were obtained in a CaCu_2.90Mg_0.10Ti_4.2O₁₂ ceramic sintered at 1100 °C for 8 h.     

Effect of sintering temperature on microstructures and microwave dielectric properties of Ba<Subscript>2</Subscript>MgWO<Subscript>6</Subscript> ceramics

The microwave dielectric properties of Ba₂MgWO₆ ceramics were investigated with a view to the use of such ceramics in mobile communication. Ba₂MgWO₆ ceramics were prepared using the conventional solid-state method with various sintering temperatures. Dielectric constants (? _r ) of 16.8–18.2 and unloaded quality factor (Q _u  × f) of 7000–118,200 GHz were obtained at sintering temperatures in the range 1450–1650 °C for 2 h. A maximum apparent density of 6.76 g/cm³ was obtained for Ba₂MgWO₆ ceramic, sintered at 1650 °C for 2 h. A dielectric constant (? _r ) of 18.4, an unloaded quality factor (Q _u  × f) of 118,200 GHz, and a temperature coefficient of resonant frequency (τ _f ) of ?34 ppm/°C were obtained when Ba₂MgWO₆ ceramics were sintered at 1650 °C for 2 h.     

Effect of excess Bi content on electrical properties of BiFe<Subscript>0.95</Subscript>Cr<Subscript>0.05</Subscript>O<Subscript>3</Subscript> thin films

The Bi_1?+?xFe_0.95Cr_0.05O₃ (BFCO) (x?=?0, 5, 10, 15 and 20%) thin films are fabricated on FTO/glass substrate using a chemical solution deposition method and sequential-layer annealing process. The effects of the excess Bi content on crystalline structure, morphology, and electrical performance of BFCO thin films are investigated. All the BFCO thin films are crystallized into polycrystalline perovskite structure and belonging to the space group of R3c. The BFCO thin films with 5 and 10% excess Bi contents possess no impurity phase. Especially, a dense surface morphology and columnar crystal structure can be obtained for the film with 5% excess Bi content. Especially, the one possesses superior ferroelectricity with a relative high remnant polarization (P _r) of 69.8 µC/cm² and low coercive electric field (E _c) of 291 kV/cm at 1 kHz due to the relatively low leakage current density of 3.04?×?10^??5 A/cm² at 200 kV/cm.     

Structure,dielectric and ferroelectric properties of lead free (K,Na)(Nb)O<Subscript>3</Subscript>-xBiErO<Subscript>3</Subscript> piezoelectric ceramics

The effect of BiErO₃ (BE) as a doping material on the structural, dielectric and ferroelectric properties of (KNa)NbO₃ ceramics was explored in this research. Co-existence of two phase regions was confirmed in the composition range at x?=?0.5% and x?=?1.0%. The addition of BE content led to a decrease of the grain size and the ceramics became denser. Bulk P–E hysteresis loops were obtained with a maximum polarization of P _max = 30.56 µC/cm² and a remnant polarization of P _r = 25.10 µC/cm², along with a coercive field of E _c  ~ 11.26 kV/cm. The results revealed that a field strain value of ~?0.26 for x?=?0.5% of BE substitution was attained. This presents outstanding piezoelectric and dielectric properties.     

Effects of NiNb<Subscript>2</Subscript>O<Subscript>6</Subscript> doping on dielectric property,microstructure and energy storage behavior of Sr<Subscript>0.97</Subscript>La<Subscript>0.02</Subscript>TiO<Subscript>3</Subscript> ceramics

Sr_0.97La_0.02TiO₃ ceramics with samll amounts of NiNb₂O₆ additives were prepared by the traditional solid state sintering method, and the phase purity, microstructure, dielectric properties and energy storage behavior of the NiNb₂O₆-added Sr_0.97La_0.02TiO₃ ceramics were investigated. The results show that the grain size of the ceramics firstly decreases and then increases with increasing NiNb₂O₆ concentration. The average grain size reaches 0.55 um for the sample with 4.5 wt% NiNb₂O₆. Moreover, impedance spectroscopy (IS) analysis was employed to study the electrical conductive behavior of NiNb₂O₆-doped Sr_0.97La_0.02TiO₃ ceramics. IS results reveale that the NiNb₂O₆-doped Sr_0.97La_0.02TiO₃ ceramic has large R _gb /(R _gb  + R _g ) ratios due to the decreased grain sizes. The breakdown strength is notably improved, and the highest breakdown strength of 324 kV/cm can be achieved for the sample with 4.5 wt% NiNb₂O₆ additive. The Sr_0.97La_0.02TiO₃ sample with 4.5 wt% NiNb₂O₆ possesses the maximum theoretical energy density of 1.36 J/cm³, which is about 2 times higher than that of pure SrTiO₃ in the literature. And its energy storage efficiency reaches 91.4 % under applied electric field of 80 kV/cm. This study provides the NiNb₂O₆ added ceramic as an attractive candidate for making high-energy density capacitors.     

Effects of sintering temperature on the properties of Mn/Y codoped Ba<Subscript>0.67</Subscript>Sr<Subscript>0.33</Subscript>TiO<Subscript>3</Subscript> ceramics for tunable application

(Ba_0.67Sr_0.33)_1?3x/2Y _x Ti_1?y/2Mn _y O₃ [BST(Mn + Y), x = 0.006, y = 0.005] ceramics were fabricated by using citrate–nitrate combustion derived powder. Microstructure and dielectric properties of the BST(Mn + Y) ceramic samples were investigated within the sintering temperature ranged from 1220 to 1300 °C. Sintering temperature has a great influence on the microstructure and electrical properties of the ceramic samples. The dielectric properties, ferroelectric properties, and tunability are enhanced by optimizing sintering temperature. The relatively high tunability of 40 % (1.5 kV/mm DC field, 10 kHz) was obtained, and relatively low dielectric loss, <0.0052 (at 10 kHz, 20 °C) was acquired for BST(Mn + Y) samples sintered at 1275 °C for 3 h. Both the low dielectric loss and enhanced tunable properties of BST(Mn + Y) are useful for tunable devices application.     

Scaling behavior of dynamic hysteresis in Bi<Subscript>3.15</Subscript>Nd<Subscript>0.85</Subscript>Ti<Subscript>3</Subscript>O<Subscript>12</Subscript> ceramics

The scaling behavior of dynamic hysteresis was investigated in Bi_3.15Nd_0.85Ti₃O₁₂ bulk ceramics at a frequency of 1–1000 Hz and an external electric field amplitude of 79–221 kV/cm. The scaling behavior at low amplitude (E ₀ ≤ 114 kV/cm) takes the form of \(\langle A \rangle \propto f^{ - 0.013} E_{0}^{0.7}\) for low frequency (f ≤ 200 Hz) and \(\langle A \rangle \propto f^{ - 0.013} E_{0}^{0.22}\) for high frequency (f > 200 Hz), where \(\langle A \rangle\) is the area of hysteresis loop and f and E ₀ are frequency and amplitude of external electric field, respectively. At high amplitude (E ₀ > 114 kV/cm), we obtain \(\langle A \rangle \propto f^{0.011} E_{0}^{1.163}\) at low frequency and \(\langle A \rangle \propto f^{ - 0.015} E_{0}^{0.7}\) at high frequency. At low E ₀, the contribution to the scaling relation mainly results from reversible domain switching, while at high E ₀ reversible and irreversible domain switching concurrently contribute to the scaling relation.     

Low temperature sintering and microwave dielectric properties of Zn<Subscript>3</Subscript>Mo<Subscript>2</Subscript>O<Subscript>9</Subscript> ceramic

Crystal structure and dielectric properties of Zn₃Mo₂O₉ ceramics prepared through a conventional solid-state reaction method were characterized. XRD and Raman analysis revealed that the Zn₃Mo₂O₉ crystallized in a monoclinic crystal structure and reminded stable up to1020 °C. Dense ceramics with high relative density (~ 92.3%) were obtained when sintered at 1000 °C and possessed good microwave dielectric properties with a relative permittivity (ε _r ) of 8.7, a quality factor (Q?×?f) of 23,400 GHz, and a negative temperature coefficient of resonance frequency (τ _f ) of around ??79 ppm/°C. With 5 wt% B₂O₃ addition, the sintering temperature of Zn₃Mo₂O₉ ceramic was successfully lowered to 900 °C and microwave dielectric properties with ε _r ?=?11.8, Q?×?f?=?20,000 GHz, and τ _f = ??79.5 ppm/°C were achieved.     

Microwave dielectric properties of Bi(Sc<Subscript>1/3</Subscript>Mo<Subscript>2/3</Subscript>)O<Subscript>4</Subscript> ceramics for LTCC applications

A novel microwave dielectric ceramics Bi(Sc_1/3Mo_2/3)O₄ with low firing temperature were prepared via the solid reaction method. The specimens have been characterized using scanning electron microscopy, X-ray diffraction, Raman spectroscopy and DC conductivity. The Bi(Sc_1/3Mo_2/3)O₄ ceramics showed B-site ordered Scheelite-type structure with space group C2/c. Raman analysis indicated that prominent bands were attributed to the normal modes of vibration of MoO₄ ^2? tetrahedra. The dielectric loss of Bi(Sc_1/3Mo_2/3)O₄ ceramics can be depended strongly the bulk conductivity by DC measurement. The superior microwave dielectric properties are achieved in the Bi(Sc_1/3Mo_2/3)O₄ ceramic sintered at 875 °C/4 h, with dielectric constant?~?25, Q?×?f ~?51,716 GHz at 6.4522 GHz and temperature coefficient of resonance frequency ~???70.4 ppm/°C. It is a promising microwave dielectric material for low-temperature co-fired ceramics technology.     

Crystal structure,microstructure and microwave dielectric properties of novel MgAl<Subscript>2</Subscript>Ti<Subscript>3</Subscript>O<Subscript>10</Subscript> ceramic

In the present work, a novel MgAl₂Ti₃O₁₀ ceramic was obtained using a traditional solid-state reaction method. X-ray diffraction and energy dispersive spectrometer showed that the main MgAl₂Ti₃O₁₀ phase was formed after sintered at 1300–1450 °C. With rising the sintering temperature from 1300 to 1450 °C, the bulk density (ρ), relative permittivity (ε _r ) and Q?×?f value firstly increased, reached the maximum values (3.61 g/cm³, 14.9, and 26,450 GHz) and then decreased. The temperature coefficient of resonator frequency (τ _f ) showed a slight change at a negative range of ??94.6 to ??83.7 ppm/°C. When the sintering temperature was 1400 °C, MgAl₂Ti₃O₁₀ ceramics exhibited the best microwave dielectric properties with Q?×?f?=?26,450 GHz, ε _r ?=?14.9 and τ _f ?=???83.7 ppm/°C.     

Effect of Ni<Superscript>2+</Superscript> substitution on crystal structure and microwave dielectric properties for MgZrNb<Subscript>2</Subscript>O<Subscript>8</Subscript> ceramics

Monoclinic structured Mg_1?xNi_xZrNb₂O₈ (0?≤?x?≤?0.12) ceramics were synthesized for the first time through traditional solid-state reaction process and pure phase were obtained in all range. Rietveld refinement was used to analyze the crystal structure. With the increase of Ni²⁺ substitution amount, ε _r decreased, Q?×?f rose first then fell, τ _f shifted for the positive direction. Bond ionicity, lattice energy and bond energy were separately calculated to investigate the correlations with microwave dielectric properties. Typically, ceramics samples with the composition of Mg_0.92Ni_0.08ZrNb₂O₈ sintered at 1280 °C for 4 h exhibited the optimum microwave dielectric properties: ε _r ?=?24.58, Q?×?f?=?74534.1 GHz, τ _f ?=???49.11 ppm/°C, which could be a promising material for application.     

Effects of Cr<Subscript>2</Subscript>O<Subscript>3</Subscript> doping on the microstructure and electrical properties of (Ba,Ca)(Zr,Ti)O<Subscript>3</Subscript> lead-free ceramics

Lead-free ceramics (Ba_0.85Ca_0.15)(Zr_0.1Ti_0.9)O₃?x wt.%Cr₂O₃ (BCZT-xCr) were prepared via the conventional solid-state reaction method. The microstructure and electrical properties of BCZT-xCr samples were systematically studied. XRD and Raman results showed that all samples possessed a single phased perovskite structure and were close to the morphotropic phase boundary (MPB). With the increase of the Cr content, the rhombohedral-tetragonal phase transition temperature (T _R-T) increases slightly, and the Curie temperature (T _C) shifts towards the low temperature side. XPS analysis reveals that Cr³⁺ and Cr^{5 +} ions co-existed in Cr-doped BCZT ceramics, indicating the different impact on the electrical properties from Cr ions as “acceptor” or “donor”. For the x = 0.1 sample, relative high piezoelectric constants d ₃₃ (～316 pC/N) as well as high Q _m (～554) and low tanδ (～0.8%) were obtained. In addition, the AC conductivity was also investigated. Hopping charge was considered as the main conduction mechanism at low temperature. As the temperature increases, small polarons and oxygen vacancies conduction played important roles.     

Large enhancement of upconversion luminescence in Er<Superscript>3+</Superscript>/In<Superscript>3+</Superscript>:Ba<Subscript>0.85</Subscript>Ca<Subscript>0.15</Subscript>TiO<Subscript>3</Subscript> lead-free piezoelectric ceramics

A series of In³⁺-doped Ba_0.85Ca_0.15TiO₃:0.75%Er³⁺/xIn³⁺ (BCT:Er/xIn) lead-free piezoelectric ceramics with excellent upconversion luminescence were synthesized by the solid state reaction method. The effects of In³⁺ content on the crystal structure, ferroelectric, dielectric, piezoelectric, and upconversion luminescence properties were systematically studied. Under 980 nm excitation, a giant enhancement of the green emission (550 nm) by 10 times is achieved upon 2.5% mol In³⁺ doping, which is rarely observed in rare-earth ions-doped perovskite ferroelectric materials. The ultraviolet-visible-near infrared absorption measurements show that the In³⁺ doping may improve the dissolution of Er³⁺ ions and modify the isolate-/clustered-Er³⁺ ratio for x?≤?2.5%, resulting in the enhancement of the absorption cross-section, thereby contributing to the enhancement of green luminescence. Unfortunately, the In³⁺ doping suppresses the ferroelectric and piezoelectric properties of the BCT:Er/xIn ceramics. This problem can be resolved by adding a small amount (1 mol%) of Yb³⁺ to the BCT:Er/xIn ceramics to restore their good ferroelectric and piezoelectric properties. Such In³⁺ and rare-earth ions co-doped ceramics with greatly enhanced upconversion luminescence and good ferroelectricity and piezoelectricity may have potential applications in electro-optical devices.     

Low temperature sintering and dielectric properties of Ba<Subscript>3</Subscript>(VO<Subscript>4</Subscript>)<Subscript>2</Subscript> microwave ceramics using Co<Subscript>2</Subscript>O<Subscript>3</Subscript> additives

The Ba₃(VO₄)₂–x wt% Co₂O₃ (x?=?0.5–5) ceramics were prepared by the solid state reaction method in order to reduce the sintering temperature. The effects of the Co₂O₃ additions on the phase composition, microstructures, sintering characteristics and microwave dielectric properties of Ba₃(VO₄)₂ ceramics are investigated by an X-ray diffractometer, a scanning electron microscope and a network analyzer. As a result, the Q?×?f value of 54,000 GH, the ε _r of 14.6 and the τ_f value of +58.5 ppm/°C were obtained in the sample of the Ba₃(VO₄)₂–3 wt% Co₂O₃ ceramic sintered at the temperature of 925 °C, which is capable to co-fire with electrode metal of high conductivity such as Ag (961 °C). Moreover, the Q?×?f values of the sample with Co₂O₃ higher than that of 3 wt% additions decreased because of the formation of Ba₂V₂O₇ phase.     

Synthesis,microstructure, and electrical behavior of (Na<Subscript>0.5</Subscript>Bi<Subscript>0.5</Subscript>)<Subscript>0.94</Subscript>Ba<Subscript>0.06</Subscript>TiO<Subscript>3</Subscript> piezoelectric ceramics via a citric acid sol–gel method

Nanosize (Na_0.5Bi_0.5)_0.94Ba_0.06TiO₃ precursor powders were prepared via the citric acid sol–gel method. The ceramics were sintered at 1100–1150 °C. All ceramics exhibit a single-phase perovskite structure. With increasing sintering temperature, the average size of grains in the samples changes slightly from 0.3 to 0.5 µm. All ceramics show obvious dielectric dispersion. Activation energy values were obtained via impedance, electric modulus, and conductivity, respectively, which are in the range of 0.60–1.06 eV. Compared to ceramics synthesized by solid-state reaction method, the as-synthesized samples are fine-grained and have high depolarization temperature and excellent temperature stability of the piezoelectric constant (d ₃₃). The d ₃₃ value of the sample sintered at 1120 °C remains as high as 119 pC N^?1 with increasing annealing temperature to 115 °C, whereas the reduced amplitude of d ₃₃ is only approximately 3%.     

Microstructure and properties of lead-free (Bi<Subscript>1/2</Subscript>Na<Subscript>1/2</Subscript>)TiO<Subscript>3 </Subscript>based piezoelectric ceramics doped with different cations

Different cations doped lead-free piezoelectric (Bi_1/2Na_1/2)TiO₃ ceramics with the general formula Na_0.4995Bi_0.4995Ba_0.001Ti_0.998M_0.002O₃ (M = Nb, Ta, and Sb) were fabricated. The effects of processing parameters and doping on phase content, microstructure, dielectric and piezoelectric properties of the materials were discussed. Experimental results show that Nb doped (Bi_1/2Na_1/2)TiO₃ exhibits superior polarization performance over the existing lead-free ceramics with a d₃₃ value of 122 pC/N obtained when poled at 60 kV/cm at room temperature. The best piezoelectric properties were achieved in (Bi_1/2Na_1/2)TiO₃ doped with Ta having a measured d₃₃ value of 164 pC/N for samples poled at 100 °C under the applied field of 50 kV/cm.