Influence of sintering temperature on microstructure and electric properties of CuO doped alkaline niobate-based lead-free ceramics

In this work, microstructure characteristics, dielectric, piezoelectric and ferroelectric properties of lead-free (K_0.4425Na_0.52Li_0.0375)(Nb_0.87Ta_0.06Sb_0.07)O₃ (KNLNST) doped with 1?mol% copper oxide (CuO) piezoelectric ceramics prepared by a conventional solid-state reaction route are investigated with an emphasis on the influence of sintering temperature. The introduction of CuO could significantly improve the sinterability of KNLNST ceramics. It is found that the tetragonality of the ceramics increases with raising sintering temperature. A dense microstructure with increased grains is developed, probably due to liquid-phase sintering. Both the piezoelectric constant d ₃₃ and planar electromechanical coupling k _p increase with increasing relative density and grain size. The Curie temperature T _C values increase slightly when the sintering temperature is increased. In addition, the KNLNST ceramics doped with 1?mol% CuO show obvious dielectric relaxor characteristics, and the relaxor behavior of ceramics is strengthened by increasing the sintering temperature. The improved piezoelectric and dielectric properties of d ₃₃?=?241?pC/N, k _p?=?0.437, dielectric loss tanδ?=?0.0087, mechanical quality factor Q _m?=?138, dielectric constant ε _r?=?1,304 can be obtained for specimens sintered at 1,080?°C for 3?h.     

Effect of CuO addition on structure and electrical properties of low temperature sintered quaternary piezoelectric ceramics

The ceramics were prepared successfully by CuO additions to Pb[(Mn_1/3Sb_2/3)_0·06(Ni_1/2W_1/2)_0·02(Zr_0·49Ti_0·51)_0·92]O₃. Effect of the addition on sintering temperature, structure and electrical properties of ceramics was investigated. The piezoelectric ceramics was prepared by solid-state reaction. Sintering experiments were accomplished at temperature between 950 and 1100 °C added 0· 3–1· 0 wt% CuO. The sintering temperature was reduced from 1250 °C (without CuO additions) to 970 °C when CuO-doped. The ceramics sintered at 970 °C for 2 h with 0· 7 wt% CuO exhibited ε _r = 1845, tan δ = 0· 15%, d ₃₃ = 395 pC/N, k _p = 0· 58 and Q _m = 1830, which were the highest values. With increasing CuO doping, T _c becomes lower. Jahn–Teller effect was used to explain the contraction of c-axis and simultaneous extension of a-axis in the lattice.     

Phase stability, low temperature cofiring and microwave dielectric properties of BaTi5O11 ceramics with BaCu(B2O5) addition

The effects of BaCu(B₂O₅) (BCB) additions on the sintering temperature, microstructure and microwave dielectric properties of BaTi₅O₁₁ modified with 1.0 wt% CuO (BTC) ceramic have been investigated using X-ray diffraction, scanning electron microscopy and dielectric measurement. The BTC ceramic shows a high sintering temperature (~1,100 °C) and good microwave dielectric properties as Q × f = 44,530 GHz, ε _r = 40.5, τ _f  = 39 ppm/°C. The addition of BCB to BTC effectively reduced the sintering temperature from 1,100 to 925 °C. The reduced sintering temperature was attributed to the BCB liquid phase. The BTC ceramic doped with 4 wt% BCB has a good microwave dielectric properties with Q × f = 25,502 GHz, ε _r = 37.4, τ _f  = 33.1 ppm/°C. The chemical compatibility of silver electrodes and low-fired samples has also been investigated.     

Dielectric and electromechanical properties of Mn-doped 0.2875 Pb(Mg1/3Nb2/3)O3–0.2875 Pb(Yb1/2Nb1/2)O3–0.425 PbTiO3 ceramics

In this study, 0.2875 Pb(Mg_1/3Nb_2/3)O₃–0.2875 Pb(Yb_1/2Nb_1/2)O₃–0.425 PbTiO₃ (0.2875PMN–0.2875PYbN–0.425PT) ternary ceramic composition was doped with 1 mol% MnCO₃ in order to induce hard character for potential high-power applications. Dense 0.2875PMN–0.2875PYbN–0.425PT ceramics with 1 mol% MnCO₃ addition were fabricated after sintering at 1100 °C. ε _r = 1728, tanδ = 0.35 %, d ₃₃ = 320 pC/N, d ₃₁ = ?103 pC/N, Q _m = 467, k _p = 0.40, k ₃₁ = 0.24, k ₃₃ = 0.49, and T _c = 280 °C were measured for Mn-doped ceramics. However, undoped ceramics had ε _r = 2380, tanδ = 1.95 %, d ₃₃ = 433 pC/N, d ₃₁ = ?145 pC/N, Q _m = 60, k _p = 0.43, k ₃₁ = 0.27, k ₃₃ = 0.48, and T _c = 285 °C. Acceptor Mn²⁺/Mn³⁺ ions presumably substituted B-site ions in the perovskite structure and formed defect dipole pairs. The electrically “hard” character was induced as a result of the domain wall pinning due to the existing defect pairs. Particularly, increasing Q _m from 60 to 467 and decreasing tanδ from 1.95 to 0.35 % after Mn doping showed that Mn-doped 0.2875PMN–0.2875PYbN–0.425PT ceramics with “hard” character are potential candidates for high-power projector and transducer applications.     

Phase structures and electrical properties of LiSbO3 doped 0.994K0.5Na0.5NbO3–0.004K5.4Cu1.3Ta10O29–0.002BiMnO3 piezoelectric ceramics

LiSbO₃ (LS) doped 0.994K_0.5Na_0.5NbO₃–0.004K_5.4Cu_1.3Ta₁₀O₂₉–0.002BiMnO₃ (KNN–KCT–BM) piezoelectric ceramics with excellent properties have been fabricated by conventional ceramic processing. It is found that the dopant of LS has considerable effect on the grain size, phase structure and electrical properties of KNN–KCT–BM ceramics. The KNN–KCT–BM ceramics doped with 4.5 mol% LS ceramics show good electrical properties such as d ₃₃ = 208 pC/N, Q _m  = 95, k _p  = 40.5 %, T _c  = 335 °C, T _o?t  = 55 °C, ε _r  = 1,190 and rather low dielectric dissipation of tanδ = 1.25 % (1 kHz) and tanδ < 1 % (100 kHz). This indicates that 4.5 mol% LS-doped KNN–KCT–BM piezoceramic is an alternative lead-free piezoelectric material for the development of piezoelectric devices working at high temperature.     

Optimized sintering properties and temperature stability of MgZrTa<Subscript>2</Subscript>O<Subscript>8</Subscript> ceramics with CuO addition for microwave application

Microwave dielectric ceramics CuO–modified MgZrTa₂O₈ were synthesized by the conventional solid-state reaction method. The effects of CuO additives on the sintering characteristics and microwave dielectric properties have been investigated. With CuO addition, the sintering temperature of MgZrTa₂O₈ ceramics can be effectively lowered from 1475 to 1375 °C without decreasing its dielectric properties obviously and the temperature coefficient of the resonant frequency of MgZrTa₂O₈ ceramics have been optimized to near-zero. The crystalline phase exhibited a wolframite crystal structure and no second phase was detected at low addition levels. The grain growth of CuO–modified MgZrTa₂O₈ ceramics was accelerated due to liquid phase effect. The relative dielectric constants (ε_r) were correlated with apparent density and were not significantly different for all levels of CuO concentration. The quality factors (Q?×??) and temperature coefficient of resonant frequency (τ_?), which were strongly dependent on the CuO concentration, were analyzed by the grain size and the dielectric constant respectively. A best Q?×?? value of 116400 GHz and τ_? value of ?6.19 ppm/℃ were obtained for specimen with 0.05 wt% CuO addition at 1375 °C.     

Structure and energy storage properties of Ti vacancies charge compensated Re 2O3-doped SrTiO3 (Re = Pr, Nd, Gd) ceramics

By introducing Ti vacancies in advance for charge compensation, single cubic perveskite rare-earth doped strontium titanate ceramics with the formula Re _0.02Sr_0.98Ti_0.995O₃ (Re–STO, Re = Pr, Nd, Gd) were prepared via solid-state reaction method. All Re–STO ceramics sintered at 1,410 °C in air for 3 h showed a similar dense microstructure with the grain size lower than 10 μm. The room temperature dielectric constant ε _r of Re–STO ceramics was higher than 3,000 (@ 1 kHz) and changed <8 % within the applied bias electric field. Especially, the room temperature dielectric loss tanδ of Re–STO ceramics was lower than 0.02 (@ 1 kHz), and the average breakdown strength E _b surpassed 14 kV/mm, demonstrating that Re–STO ceramics could be very promising for high-voltage capacitor applications. The temperature stability of the ε _r of Re–STO ceramics was evaluated in a temperature range of ?50 to 200 °C. Meanwhile, the energy storage density of Re–STO ceramics was investigated as a function of the applied bias electric field.     

Effects of CuO doping on the structure and properties lead-free KNN-LS piezoelectric ceramics

(0.95Na_0.5K_0.5NbO₃-0.05LiSbO₃)-x mol% CuO (KNN-LS-xCuO) lead-free piezoelectric ceramics have been fabricated by a conventional solid-state reaction route at a lower sintering temperature and the effects of CuO-dopant on structure and properties of KNN-LS ceramics have been studied. It is found that the addition of CuO significantly improves the sinterability and properties of KNN-LS ceramics. X-ray diffraction data shows that a small amount of CuO does not change the phase structure of KNN-LS and a dense microstructure with smaller and more uniform grains is developed, probably due to liquid-phase sintering. With the increase of CuO content x, the relative density, d ₃₃ , k _p , tanδ and Q _m have been improved obviously when x < 0.45 due to the presence of the liquid phase and the refined grains, but excessive CuO would degrade the comprehensive properties of KNN-LS-xCuO ceramics. The best specimen with a high relative density of 98.53 % was fabricated when x = 0.45 at 1,060 °C, relating constants respectively are: d ₃₃  = 175pC/N, k _p  = 0.46, ε _r  = 551.23, tanδ = 1.41 %, Q _m  = 41.5.     

Effects of cobalt and sintering temperature on electrical properties of Ba0.98Ca0.02Zr0.02Ti0.98O3 lead-free ceramics

Lead-free (Ba_0.98Ca_0.02)(Zr_0.02Ti_0.98)O₃-xmol% (x = 0–1.6) cobalt ceramics (BCZT-xCo) have been fabricated by the traditional solid-state reaction technique and the effects of Co and sintering temperature on ferroelectric, dielectric and piezoelectric properties of (Ba_0.98Ca_0.02)(Zr_0.02Ti_0.98)O₃ lead-free ceramics have been studied systematically. The orthorhombic–tetragonal (T _O–T) transition shift towards lower temperature with increasing Co addition, while Curie temperature (T _c) remained at relatively high value of 107 °C. And the Main piezoelectric parameters are optimized at x = 0.8 mol% with a high piezoelectric coefficient (d ₃₃ = 330 pC/N), a planar mode electromechanical coupling factor (k _p = 46.7 %), a high dielectric constant (ε _r = 2,675) and a low dielectric loss (tanδ = 0.90 %) at 1kHZ. Besides these, high remnant polarization (P _r) and low coercive field (E _c) of 11.5 μC/cm², 0.31 kV/cm are also obtained at (Ba_0.98Ca_0.02)(Zr_0.02Ti_0.98)O₃-0.8 mol%Co lead-free ceramics. Furthermore, greatly enhanced temperature stability of the piezoelectric properties was obtained in the temperature range from 20 to 90 °C. The above results indicate that BCZT-Co ceramics are promising lead-free materials for practical applications.     

Studies of structural and dielectric properties of Ba5BiTi3Nb7O30 ceramics

The polycrystalline samples of Ba₅BiTi₃Nb₇O₃₀ (hereafter BBTN) belonging to ferroelectric oxide family of tungsten bronze structure were prepared by high temperature solid-state reaction method. Preliminary X-ray analysis of the samples provided the lattice parametersa=11·9331 Å,b=14·9684 Å, andc=7·0193 Å, and also formation of a single-phase orthorhombic structure at room temperature (303 K). Detailed studies of dielectric constant (ε) and loss (tanδ) as a function of frequency (500 Hz to 10 KHz) at room temperature and also as a function of temperature (liquid nitrogen to 160°C) show the dielectric anomaly and structural phase transition at 16·8°C.     

Microstructure and enhanced electrical properties of (1−x)(Na0.5K0.44Li0.06)NbO3–x(Ba0.85Ca0.15)(Zr0.10Ti0.90)O3 lead-free ceramics

Environment-friendly lead-free piezoelectric ceramics (1?x)(Na_0.5K_0.44Li_0.06)NbO₃–x(Ba_0.85Ca_0.15)(Zr_0.10Ti_0.90)O₃ doped with 1.0 mol% MnO₂ were synthesized by conventional solid-state sintering method. The phase transition behavior and electrical properties of the ceramics is systemically investigated. It was found that all the ceramics formed pure perovskite phase with 0.0 ≤ x ≤ 0.1, and the phase structure of the ceramics gradually transformed from orthorhombic to tetragonal phase with increasing x. Coexistence of the orthorhombic and tetragonal phase is formed in the ceramics with 0.04 ≤ x ≤ 0.06 at room temperature, and enhanced dielectric, ferroelectric and piezoelectric properties are achieved in the two phase’s region. The ceramics in the mixed phase region exhibits the following optimum electrical properties: d ₃₃  = 130–147 pC/N, ε _r  = 642–851, P _r  = 5.51–12.44 μC/cm². The Curie temperature of the ceramics with mixed phase region was found to be 353–384 °C. The significantly enhanced dielectric properties, ferroelectric properties and piezoelectric properties with high cubic-tetragonal phase transition temperatures (T _c ) make the KNLN–xBCZT ceramics showing the promising lead-free piezoelectrics for the practical applications.     

Effects of LiF addition on the sintering behavior and microwave dielectric properties of Li<Subscript>2</Subscript>Mg<Subscript>3</Subscript>SnO<Subscript>6</Subscript> ceramics

Li₂Mg₃SnO₆ (abbreviation for LMS) ceramics doped with 1–4 wt% lithium fluoride (LiF) were prepared by the conventional solid-state reaction method. The effects of LiF addition on the phase compositions, sintering behaviors and microwave dielectric properties of LMS ceramics were investigated. A small amount of LiF addition could effectively decrease the sintering temperatures due to the liquid phase in the sintering process and induced no apparent degradation of the microwave dielectric properties. The optimized quality factor values for each composition firstly increased and then decreased with the increase of the LiF content. Whereas, the optimized dielectric permittivity increased with increasing of the LiF content. Distinguished microwave dielectric properties with a dielectric constant (ε _r) of 11.13, a quality factor (Q·f) of 104,750 GHz, and a temperature coefficient of resonant frequency (τ _f ) of ?10.83 ppm/°C were obtained for LMS ceramics sintered at 950?°C doped with 3 wt% LiF, which showed that the materials were suitable for the low temperature co-fired ceramics applications (LTCC).     

Effects of MnO2 doping on microstructure and microwave dielectric properties of Ba4.2Nd9.2Ti18O54–NdAlO3 ceramics

MnO₂ doped Ba_4.2Nd_9.2Ti₁₈O₅₄–NdAlO₃(13 wt%) (BNT–NA) microwave dielectric ceramics with the near zero τ _f and the wide range of sintering temperature were prepared by conventional solid state method. The effects of Mn⁴⁺ doping on the microstructures and microwave dielectric properties of BNT–NA ceramics were investigated. XRD patterns showed only a single BaNd₂Ti₅O₁₄ phase was identified in all samples and there was no second phase. The sintering temperature decreased from 1,380 to 1,320 °C as MnO₂ content increased from 0.1 to 0.9 wt%. The MnO₂ doped BNT–NA ceramics could be densified at a lower sintering temperature. The MnO₂ additive had a positive effect on lowing sintering temperature of BNT–NA ceramics. The τ _f varied from negative to positive with the increase of MnO₂. Excellent microwave dielectric properties were achieved in Ba_4.2Nd_9.2Ti₁₈O₅₄–NdAlO₃ ceramics doped with 0.3 wt% MnO₂ and sintered at 1,380 °C for 2 h: ε _r  = 66.5, Q × f = 13,948 GHz, τ _f  = 0.4 ppm/°C.     

Low temperature sintering and microwave dielectric properties of Li2ZnSiO4 ceramics with ZB glass

The influence of zinc borate (ZB) glass on densification, phase composition, microstructure and microwave dielectric properties of Li₂ZnSiO₄ ceramics has been investigated by using X-ray diffraction, scanning electron microscopy and Advantest network analyzer. Undoped Li₂ZnSiO₄ ceramics exhibited good microwave dielectric properties of ε _r  = 5.8, Q × f = 14,700 GHz and τ _f  = ?96.6 ppm/°C. When ZB glass was added, the sintering temperature of Li₂ZnSiO₄ ceramics was effectively reduced to 950 °C. Addition of 25.wt% ZB glass to Li₂ZnSiO₄ ceramics sintered at 950 °C showed excellent dielectric properties of ε _r  = 5.5, Q × f = 10,800 GHz (f = 6.8 GHz) and τ _f  = ?47.2 ppm/°C. Moreover, the material was compatible with Ag electrodes, making it a very promising candidate material for LTCC applications.     

Low temperature sintering and microwave dielectric properties of 7NiNb2O6–9TiO2 ceramics with CuO addition

The effects of CuO additive on sintering temperature and microwave dielectric properties of 7NiNb₂O₆–9TiO₂ ceramics prepared by solid-state reaction method have been investigated. The phases and microstructure have also been evaluated using X-ray diffraction and scanning electron microscopy. The pure 7NiNb₂O₆–9TiO₂ ceramics show a high sintering temperature of about 1,200?°C. However, the addition of CuO lowered the sintering temperature of 7NiNb₂O₆–9TiO₂ ceramics from 1,200 to 935?°C due to the CuO liquid-phase. The results showed that the microwave dielectric properties were strongly dependent on densification, crystalline phases and grain size. The 7NiNb₂O₆–9TiO₂ ceramics with the addition of 3.2 wt% CuO sintered at 935?°C afforded excellent dielectric properties of ε _r ?=?60.5, Q?×?f?=?10,039?GHz (at 3.8?GHz) and τ _f ?=?62?ppm/°C, which represented very promising candidates for LTCC dielectric materials.     

Effects of BaNb2O6 addition on microstructure and dielectric properties of BaTiO3 ceramics

(1 ? x)BaTiO₃–xBaNb₂O₆ [(1 ? x)BT–xBN] ceramics with x = 0, 0.005, 0.008, 0.01, 0.02, 0.03 were prepared by a conventional solid-state reaction route. The effect of BN addition on phase composition, microstructure and dielectric properties of BT-based ceramics were investigated by X-ray diffraction, scanning electron microscope and impedance spectroscopy. The results showed that a systematic structure change from the ferroelectric tetragonal phase to pseudo-cubic phase was observed near x = 0.01 at room temperature. It resulted in a considerable change of density, grain size and dielectric properties of the samples when BN was introduced. Meanwhile, it also lowered the sintering temperature of the ceramics. The dielectric constant peak and the variation rate of capacitance at Curie temperature are markedly depressed and broaden with increasing BN content. Especially, the ceramics with x = 0.008 and x = 0.01 showed good dielectric properties over the measured temperature range. Optimal dielectric properties of ε = 3,851, tanδ = 0.7 % at room temperature and Δε/ε₂₅ ≤ ±6.8 % (?55 to 125 °C) were obtained for the BT-based ceramics doped with 0.8 mol% BN, which was obviously superior to BaTiO₃ and BaNb₂O₆ ceramic, and it met the requirements of EIA X7R specifications.     

Lead-free (Ba0.7Ca0.3)TiO3-Ba(Zr0.2Ti0.8)O3-xwt %CuO ceramics with high piezoelectric coefficient by low-temperature sintering

Lead-free (Ba_0.7Ca_0.3)TiO₃-Ba(Zr_0.2Ti_0.8)O₃-xwt %CuO(BCZT-xCu) piezoelectric ceramics have been fabricated by the solid-state reaction process and the effects of CuO addition on the phase structure and piezoelectric properties of the ceramics have been studied. Our results reveal that the addition of CuO significantly improves the sinterability of BCZT ceramics which results in a reduction of sintering temperature from 1,540 to 1,350?°C without sacrificing the high piezoelectric properties. X-ray diffraction (XRD) data shows that CuO diffuses into the lattice of BCZT-xCu ceramics and a pure perovskite phase forms in the ceramic. SEM images indicate that a small amount of CuO addition affects the microstructure, obviously. Main piezoelectric parameters of these ceramics are optimized around x?=?0.04?wt % with a high piezoelectric coefficient (d ₃₃?=?510?pC/N), a planar electromechanical coefficient k _p of 45%, a high dielectric constant (ε _r ?=?3,762) and a low dissipation factor (tanδ?=?1.05%) at 1?kHz. The results indicate that the BCZT-xCu ceramics are promising lead-free practical applications.     

A new route to improve microwave dielectric properties of low-temperature sintered Li2TiO3-based ceramics

Low-temperature sintered Li₂TiO₃-based ceramics for low temperature co-fired ceramic resonators were synthesized by a solid state reaction method. Their microwave dielectric properties were further improved by CeO₂ addition. When the amount of CeO₂ increased, the relative permittivity (ε _r ) of the samples increased a little and then decreased. The quality factor (Q × f) of the samples was improved obviously for a higher standard reduction potential of cerium than that of titanium. The temperature coefficient of resonant frequency (τ _f ) of the samples decreased with the increase of CeO₂ addition. CeO₂ mainly existed as a secondary phase and it facilitated the sintering of the Li₂TiO₃-based ceramics. Typical microwave dielectric properties of ε _r  = 22.97, Q × f = 34,881 GHz, and τ _f  = 33.12 ppm/°C were obtained for Li₂TiO₃ + 2 wt% ZnO–B₂O₃ frit + 0.9 wt% CeO₂ ceramics sintered at 920 °C for 4 h. The addition of oxidizers was proved a promising route to improve the microwave dielectric properties of titanate ceramics sintered at low temperatures.     

Dielectric properties of La2O3-doped Ba0.8Sr0.2TiO3 ceramics

La₂O₃-doped Ba_0.8Sr_0.2TiO₃ dielectric ceramics were prepared by conventional solid state ceramic route. Scanning electron microscope was employed to observe the surface morphologies. The capacitance C and dielectric loss factor D of the samples were measured with automatic LCR Meter 4225 at 10 kHz respectively. The results show that: ε _r of the samples decreases and tgδ first decreases then increases with increasing amount of La₂O₃ doping. ε _r reaches better value, tgδ obtains the minimum value at 0.5 mol% La₂O₃. ε _r increases and tgδ decreases when sintering temperature increases. The samples doped with 0.5 mol% La₂O₃ sintered at 1,350 °C for 10 h exhibited attractive properties, including high relative dielectric constant (>4,000), low dielectric loss (16.8 × 10^?4), low temperature coefficient of relative dielectric constant(<±21 %) in the temperature range of +25 to +85 °C.     

Low-temperature sintering and microwave dielectric properties of Li2TiO3 based ceramics

New low sintering temperature and temperature-stable low-loss ceramics based on Li₂TiO₃ with lithium zinc borate (LZB) glass and LiZnNbO₄ doping have been prepared by the conventional solid-state reaction route. The effect of LZB glass addition on the sinterability, phase purity, microstructure, and microwave dielectric properties of Li₂TiO₃ ceramics has been investigated. The XRD results suggest the presence of single Li₂TiO₃ phases for LZB glass-added Li₂TiO₃ ceramics. The addition of LZB glass can effectively lower the sintering temperature to 900 °C, and does not induce much degradation of the microwave dielectric properties. Typically, the 2.0 wt% LZB glass-added ceramic sintered at 900 °C has better microwave dielectric properties of ε_r = 23.2, Q × f = 38,909 GHz, and τ _f  = 30.1 ppm/°C. Meanwhile, LiZnNbO₄ compound is selected to tune the temperature coefficient of resonant frequency (τ _f ) to near zero. It is found that the 2.0 wt% LZB glass-added Li₂TiO₃ ceramics with 35 wt% LiZnNbO₄ sintered at 925 °C have good microwave dielectric properties of ε_r = 20.7, Q × f = 19,366 GHz, τ _f  = ?0.5 ppm/°C, which can find applications in microwave devices that require low sintering temperature.