Low-Temperature Sintering and Piezoelectric Properties of Pb(Fe₂/₃W₁/₃)O₃-Doped 0.7Pb(Zr_0.46Ti_0.54)O₃–0.1Pb(Zn_1/3Nb_2/3)O₃–0.2Pb(Ni_1/3Nb_2/3)O₃ Ceramics for Free-Standing Silver-Electrode Co-Fired Multilayer Piezoelectric Devices

Abstract

In this study, the sintering behavior and electrical properties of 0.7Pb(Zr_0.46Ti_0.54)O₃ (PZT)–0.1Pb(Zn₁/₃Nb₂/₃)O₃ (PZN)–0.2Pb(Ni₁/₃Nb₂/₃)O₃ (PNN) piezoelectric ceramics with different Pb(Fe₂/₃W₁/₃)O₃ (PFW) doping contents were investigated to obtain a formulation that can be co-fired with silver (Ag) electrodes below 900 °C for multilayer ceramics. PFW was introduced as a sintering aid, which effectively reduced the sintering temperature of the ceramics from 1200 °C to 850 °C. The sample with x = 0.12 exhibited the largest average grain size of 1.72 μm, achieving excellent comprehensive properties with piezoelectric constant (d₃₃) = 477 pC/N, planar electromechanical coupling factor (k_p) = 0.68, dielectric loss tangent (tanδ) = 0.0154, and relative density of 98.2%. Furthermore, the feasibility of fabricating piezoelectric actuators based on this optimized composition was verified. Multilayer piezoelectric devices were prepared via screen printing combined with a carbon-based sacrificial layer method. No obvious interdiffusion was observed at the interface between the Ag internal electrodes and the ceramic matrix. The 9-layer device attained a high d₃₃ = 1470 pC/N and produced a large displacement of 5.5 μm (corresponding to a strain = 1.83%) with a voltage of 500 V. The thickness of the multilayer piezoelectric film was approximately 0.3 mm. Through this, the feasibility of manufacturing a multilayered actuator with an Ag electrode was confirmed through the composition of 0.58PZT–0.1PZN–0.2PNN–0.12PFW.

1. Introduction

Piezoelectric ceramics enable reversible conversion between mechanical and electrical energy and have been widely applied in piezoelectric actuators, fluid injection valves, automotive fuel injectors, ultrasonic motors, and piezoelectric transformers [1,2]. Multilayer piezoelectric ceramic devices adopt a parallel architecture of alternately stacked piezoelectric ceramic layers and internal electrodes, which superimposes and amplifies piezoelectric responses under the same driving voltage while reducing operating voltage, making them core components in micro-electro-mechanical systems (MEMS), precision actuators, and microsensors [3,4,5].

With electronic devices trending toward miniaturization, high integration, and low power consumption, these multilayer devices have attracted growing attention [6].

Ag and silver–palladium (Ag–Pd) alloys are preferred internal electrodes for their excellent conductivity [7,8]. However, conventional PZT-based ceramics require sintering temperatures above 1200 °C, far exceeding the melting point of Ag (961 °C), creating critical challenges for co-firing [9]. Thus, developing low-temperature sinterable (≤900 °C) PZT-based ceramics compatible with Ag electrodes is a key issue.

At present, incorporating low-melting-point sintering additives has become a mainstream strategy to realize low-temperature sintering of PZT-based ceramics [10,11,12,13]. For example, Hong et al. doped 0.7 wt% LiBiO₂ into PZT–PZNN ceramics, reducing the sintering temperature to 900 °C with a d₃₃ of 602 pC/N [14]. Zhang et al. used composite sintering aids (Li₂CO₃, Bi₂O₃, CuO, Sm₂O₃) to sinter PZT–PZNN at 960 °C, achieving a d₃₃ of ~550 pC/N and k_p of ~0.7 [13].

Screen printing and tape casting are primary forming methods for PZT multilayer device green bodies [8,10,15,16,17,18,19]. Tape casting is dominant due to its maturity and low-temperature co-fired ceramics compatibility, but its green tape thickness (tens to hundreds of micrometers) cannot meet microdevice requirements [14,20]. In contrast, screen printing offers superior thickness control and MEMS compatibility. Wang et al. fabricated an 11-layer device with a single-layer thickness of 45 μm via screen printing, which exhibited a strain of 0.66% under an electric field of 4 kV/mm [8].

However, screen-printed piezoelectric devices are usually substrate-constrained, leading to degraded electrical performance [8]. Main strategies for self-supported PZT thick films include carbon-based, organic-based, and mineral-based sacrificial layers [21], with the carbon-based method favored for its simplicity and no need for post-etching.

The quaternary PZT–PZN–PNN ceramic is attractive for its low dielectric constant, high piezoelectricity, and low dielectric loss [22,23,24], but its 1200 °C sintering temperature prohibits co-firing with Ag electrodes. PFW is a low-melting-point perovskite sintering aid, but research on its influence on the properties of PZT–PZN–PNN piezoelectric ceramics remains insufficient.

Accordingly, this work focuses on (0.7 − x)PZT–0.1PZN–0.2PNN–xPFW quinary ceramics. We investigated the influence of PFW on sintering behavior, crystal structure, microstructure, and electrical properties, identifying the optimal composition for dense sintering at 850 °C. Self-supporting multilayer devices were fabricated via screen printing with a carbon-based sacrificial layer, verifying its compatibility with Ag electrodes during co-firing.

2. Materials and Methods

2.1. Fabrication of Bulk Ceramics

Quinary piezoelectric ceramics with the nominal composition (0.7 − x)PZT–0.1PZN–0.2PNN–xPFW were fabricated via a two-step solid-state reaction method and liquid-phase-assisted sintering. A quaternary reference ceramic 0.7PZT–0.1PZN–0.2PNN without PFW was prepared under identical conditions for comparison.

High-purity commercial oxide powders (Nb₂O₅, ZnO, ZrO₂, Ni₂O₃, Fe₂O₃, WO₃, Pb₃O₄, TiO₂; purity ≥ 99.99%) were used as raw materials. Firstly, a portion of the B-site oxides, including Nb₂O₅, ZnO, ZrO₂, Ni₂O₃, Fe₂O₃ and WO₃, were ball-milled in deionized water at a rotation speed of 750 r/min for 4 h, dried, and pre-calcined at 1000 °C for 2 h to form B-site precursors. Subsequently, Pb₃O₄ and TiO₂ were added into the above precursors. The mixture was re-milled at 750 r/min for 4 h, dried, and calcined at 750 °C for 2 h. Finally, a further milling process was conducted at 900 r/min for 8 h to adjust the particle size.

The powder was granulated with 6 wt.% polyvinyl alcohol (PVA) and uniaxially pressed at 200 MPa into green disks (Φ10 mm, 2.5 mm thick). The green bodies were first heated at a rate of 1 °C/min to 550 °C and held for 15 min to burn out the binder, then ramped to the target sintering temperature at a rate of 7 °C/min and sintered for 4 h. Polished samples (2 mm thick) were screen-printed with Ag electrodes, fired at 850 °C for 20 min, and poled in silicone oil at 120 °C under a DC electric field of 3 kV/mm for 15 min, followed by aging for 24 h before testing.

2.2. Fabrication of Multilayer Piezoceramic Devices

Multilayer piezoelectric devices were fabricated via screen printing with a carbon-based sacrificial layer for self-supporting structure. The piezoelectric slurry was prepared by mixing 0.58PZT–0.1PZN–0.2PNN–0.12PFW powder (x = 0.12) with an organic vehicle (ethyl cellulose:terpineol = 1:10, mass ratio) at a mass ratio of 5:2, followed by magnetic stirring at 70 °C and ultrasonic dispersion for 10 min. The sacrificial layer slurry was formulated from the same organic vehicle, carbon black, and pre-synthesized PZT powder at a mass ratio of 15:1:3. Commercial E1058 Ag paste was used for internal electrodes, which is compatible with sintering temperatures of 800–900 °C.

Layer-by-layer screen printing was performed on 10 × 15 mm Al₂O₃ substrate. Firstly, the sacrificial layer with a size of 10 × 15 mm was printed. Next, the bottom Ag electrode (8 × 9 mm) was printed atop the sacrificial layer. Then, each piezoelectric layer (10 × 10 mm, ~30 μm thick) was printed in sequence, and an Ag electrode pattern (8 × 9 mm) was covered on the surface of every piezoelectric layer. All Ag electrodes were designed with a 1 mm reserved margin from the edges of the underlying piezoelectric layer so as to prevent interlayer electrical short-circuiting in the multilayer stacked structure. The multilayer green bodies were sintered via a two-step profile: slowly heated to 500 °C at a rate of 0.5 °C/min and held for 1 h for debinding, then heated to the target sintering temperature at a rate of 7 °C/min and held for 2 h. During sintering, the green bodies were buried in PZT powder to prevent deformation. The devices were poled in silicone oil at 120 °C under a DC electric field of 10 kV/mm for 15 min and aged for 24 h before testing.

2.3. Characterization and Performance Testing

The sintered density was measured by the Archimedes method using a BSA2245-CW electronic balance (Sartorius Scientific Instruments Co., Ltd., Beijing, China). The crystal phase structure was analyzed by X-ray diffraction (XRD) using a Bruker D8 Advanced diffractometer (Bruker AXS GmbH, Karlsruhe, Germany; software: Diffrac.EVA v4.2) with a 2θ scanning range of 20–90° and a step size of 0.02°. The microstructure and elemental diffusion were characterized by scanning electron microscopy (SEM) using a Hitachi S-4800 instrument (Hitachi High-Technologies Corporation, Tokyo, Japan) equipped with an energy-dispersive X-ray spectroscopy (EDS) system (Oxford X-MAX20, Oxford Instruments plc, Abingdon, UK; software: Aztec v4.4). The dielectric properties were tested using an XC2810A inductance–capacitance–resistance (LCR) meter (Xingchuang Instrument Co., Ltd., Changzhou, China) at room temperature and 1 kHz. D₃₃ was measured with a ZJ-2 quasi-static piezoelectric meter (Institute of Acoustics, Chinese Academy of Sciences, Beijing, China). The P–E hysteresis loops were collected via a WS-2000 ferroelectric tester (Radiant Technologies, Inc., Albuquerque, NM, USA; software: aixPlorer v3.0) at a frequency of 1 Hz. The mechanical quality factor (Q_m) and k_p were determined by the resonance-antiresonance method using a Keysight E4990A impedance analyzer (Keysight Technologies, Santa Rosa, CA, USA) with a frequency range of 20 Hz~10 MHz. The corresponding calculation formulas are as follows:

$${\mathrm{k}}_{\mathrm{p}}^2=2.55\sqrt{{\displaystyle \frac{{\mathrm{f}}_{\mathrm{p}}-{\mathrm{f}}_{\mathrm{s}}}{{\mathrm{f}}_{\mathrm{s}}}}}$$

(1)

$${\mathrm{Q}}_{\mathrm{m}}={\displaystyle \frac{1}{4\mathsf{\pi }\left({\mathrm{C}}_0+{\mathrm{C}}_1\right){\mathrm{R}}_1({\mathrm{f}}_{\mathrm{p}}-{\mathrm{f}}_{\mathrm{s}})}}$$

(2)

where ${\mathrm{f}}_{\mathrm{s}}$ and ${\mathrm{f}}_{\mathrm{p}}$ are the series resonant frequency and parallel resonant frequency, ${\mathrm{C}}_0$ is the static capacitance measured at 1 kHz, ${\mathrm{C}}_1$ is the dynamic capacitance and ${\mathrm{R}}_1$ is the equivalent resistance.

3. Results and Discussion

3.1. Phase Structure and Microstructure of Bulk Ceramics

Figure 1 shows the XRD patterns of PZT–PZN–PNN ceramics with different PFW contents sintered at 850 °C for 4 h. All the marked peaks belong to the perovskite phase, and no obvious secondary phase peaks were observed. This can be attributed to the two-step synthesis method adopted in this work: by implementing the separate synthesis of niobium oxide and lead oxide during the process, the formation of the lead niobate (PbNb₂O₆) secondary phase is effectively avoided.

Figure 1b shows the enlarged XRD patterns in the 2θ range of 30–32°. It can be observed that with the addition of PFW, the full width at half maximum (FWHM) of the (110) diffraction peak of the ceramics decreases to a certain extent, indicating improved crystallinity of the samples. Meanwhile, as the PFW content increases, the (110) peak shifts toward the higher 2θ region by approximately 0.4°. From the perspective of ionic radii, W⁶⁺ and Fe³⁺ ions (r(W⁶⁺) = 0.74 Å and r(Fe³⁺) = 0.63 Å) are considered to occupy the B-site of the ABO₃ perovskite structure due to their appropriate ionic radii [25]. Notably, their ionic radii are smaller than that of Zr⁴⁺ (0.79 Å), thus resulting in a reduction in unit cell size.

Figure 1c shows the enlarged XRD patterns in the 2θ range of 44–46°. It can be observed that all samples exhibit a certain degree of broadening in the (002) or (200) characteristic diffraction peaks, indicating that all samples are located near the morphotropic phase boundary (MPB) region. Furthermore, the diffraction peak of the x = 0.12 sample shows a typical feature of broadening and moderate splitting, corresponding to a state where the content ratio of tetragonal (T) and rhombohedral (R) phases is relatively close.

Figure 2a,b show the microstructures of pure PZT–PZN–PNN piezoelectric ceramics. At a sintering temperature of 1200 °C, the pure PZT–PZN–PNN ceramic exhibits uniform diamond-shaped grains with almost no pores. In contrast, when sintered at 850 °C, cubic grains with different sizes can be observed around the grain boundaries, together with some pores. This result indicates insufficient grain growth caused by the low sintering temperature.

After adding the PFW sintering additive, as shown in Figure 2c, the number of pores is significantly reduced, though some segregated particles still exist at the grain boundaries. At this composition, the liquid phase content remains insufficient, leading to local inhomogeneity in the ceramic. With a further increase in PFW content, the number of pores gradually diminishes. When x = 0.12 (as shown in Figure 2e), all pores disappear, and grain growth is most thorough at this point, with the average grain size reaching 1.72 μm.

However, as the amount of liquid phase further increases, the average grain size decreases to below 1 μm, as shown in Figure 2f–h. With increasing liquid phase content, the grain size continues to decline, and the proportion of grain boundaries gradually rises. This may be ascribed to the insufficient driving force for grain boundary migration at low sintering temperature, which prevents sufficient grain growth and causes the excess liquid phase to remain at the grain boundaries.

Figure 3a shows the SEM image of the 0.58PZT–0.1PZN–0.2PNN–0.12PFW ceramic sintered at 850 °C, and the corresponding EDS elemental mapping images (Figure 3b–j) illustrate the distribution of Nb, Pb, Zr, W, Ti, Zn, Fe, Ni, and O. All constituent elements are uniformly distributed within the ceramic. In particular, the doped W and Fe elements exhibit no obvious elemental segregation. This result is consistent with the single-phase characteristic revealed by XRD analysis.

Figure 4 shows the EDS analysis results of the sample shown in Figure 2h, with a chemical composition of 0.52PZT–0.1PZN–0.2PNN–0.18PFW. It can be observed that the grains are extensively wrapped by the liquid phase. Quantitative elemental analysis at the grain interior (Point 1) and grain boundary (Point 2) reveals that their chemical compositions are highly similar. W and Fe elements are detected at both positions. This phenomenon can be attributed to PFW forming a solid solution with the PZT–PZN–PNN ceramic matrix at low temperatures [25].

Figure 5 illustrates the influences of both sintering temperature and PFW content on the relative density of PZT–PZN–PNN ceramics sintered for 4 h. In the undoped sample, the relative density of the ceramics increases initially and then declines as sintering temperature increases, reaching a maximum of 98.05% at 1200 °C.

For low-PFW doping contents of x = 0.06–0.10, the relative density gradually increases with rising sintering temperature from 800 °C to 925 °C. In the medium doping range of x = 0.12–0.16, the relative density of the ceramics first increases and then remains nearly constant with further elevated sintering temperature. Specifically, the sample with x = 0.12 reaches a relative density of 98.2% at 850 °C, and its relative densities at 875, 900 and 925 °C are measured to be 98.1%, 98.4% and 98.5%, respectively. These results demonstrate that the relative density is only slightly affected by sintering temperatures above 850 °C. It can therefore be concluded that the optimum sintering temperature for the sample doped with 12 mol% PFW is approximately 850 °C. Such a low sintering temperature is mainly attributed to liquid-phase sintering. As indicated by the relevant phase diagram, a liquid phase can be formed between PFW and PbO at temperatures as low as 690 °C [26]. For high-PFW doping contents of x = 0.18, the relative density of the sintered samples remains nearly constant throughout the entire temperature range of 800 °C to 925 °C.

3.2. Electrical Properties

The d₃₃, k_p, relative dielectric constant (ε_r), mechanical quality factor (Q_m), and tanδ of (0.7 − x)PZT–0.1PZN–0.2PNN–xPFW ceramics with different PFW contents (sintered at 850 °C) were tested, and the results are summarized in Figure 6.

As can be observed, upon the addition of PFW, the piezoelectric and dielectric properties of the ceramics, including d₃₃, k_p, Q_m, and ε_r, are significantly enhanced and accompanied by a marked reduction in the tanδ. With increasing PFW content, both d₃₃ and ε_r first rise gradually, reaching their maximum values at x = 0.12 (d₃₃ = 477pC/N, ε_r = 2980). A further increase in PFW content beyond 12 mol% leads to a gradual decrease in both parameters.

For compositions with x < 0.14, the improvement in piezoelectric and dielectric properties is primarily attributed to the liquid phase formed during sintering, which facilitates particle rearrangement, enhances the relative density of the ceramics, and promotes grain growth. It is well established that larger grains can accommodate larger domain sizes, which in turn gives rise to enhanced electrical performance. As the PFW content continues to increase, the average grain size decreases sharply to below 1 μm, resulting in a concurrent decline in electrical properties—a trend that closely mirrors the variation in grain size.

Furthermore, the addition of PFW induces a rapid reduction in tanδ to below 0.02, which is likely attributed to the efficient elimination of pores during liquid-phase sintering.

Overall, the ceramic sample with x = 0.12 exhibits the optimal comprehensive electrical properties, with k_p = 0.68, Q_m = 83, d₃₃ = 477pC/N, ε_r = 2980, and a low dielectric loss tanδ = 0.0154.

Figure 7a shows the P–E hysteresis loops of (0.7 − x)PZT–0.1PZN–0.2PNN–xPFW ceramics sintered at 850 °C. The corresponding remnant polarization (P_r) and coercive field (E_c) as functions of PFW content are plotted in Figure 7b.

All samples are polarized to saturation under a maximum applied electric field of 30 kV/cm. It can be seen that E_c first decreases and then increases with increasing PFW content, reaching a minimum value of 8.5 kV/cm at x = 0.12. The remnant polarization P_r first increases and then decreases with increasing PFW content, achieving a maximum value of 17.6 μC/cm² at x = 0.12.

For x < 0.10, liquid-phase sintering promotes the elimination of pores and increases the effective volume fraction of grains in the ceramics, leading to an increase in P_r. In the range of x < 0.14, the liquid phase facilitates sufficient and uniform grain growth, which further increases P_r. As the PFW content further increases, the excess liquid phase cannot be incorporated into the lattice during the late sintering stage and remains at the grain boundaries. Such disordered amorphous structures cannot form ferroelectric domains, thus resulting in a decrease in P_r.

Notably, the ceramics prepared in this study exhibit the lowest sintering temperature among the reported counterparts [10,13,14,27,28,29]. In addition, from the perspective of energy conservation, low-temperature sintering can effectively reduce power consumption during the sintering process in large-scale industrial production, which is conducive to green and low-cost manufacturing of piezoelectric ceramic devices.

3.3. Multilayer Piezoelectric Device

In this work, 12 mol% PFW-doped PZT–PZN–PNN ceramics were used to fabricate parallel-structured multilayer ceramic devices with five, seven, and nine ceramic layers, respectively. A carbon-based sacrificial layer and the alternating parallel architecture of ceramic layers and Ag electrodes were prepared via screen printing.

Figure 8 shows the cross-sectional morphology and corresponding EDS elemental mapping images of the sintered multilayer device. As presented in Figure 8a, the thickness of a single ceramic layer is approximately 25 μm, and the thickness of the Ag electrode layer is about 2.5 μm. As shown in the Ag elemental mapping (Figure 8b), no obvious diffusion of Ag from the electrode into the ceramic layers is observed. The Pb element detected in the Ag electrode region in Figure 8c originates from the PZT–PZN–PNN ceramic powder added to the Ag paste, which is used to adjust the sintering shrinkage matching between the electrode and the ceramic layers. The sintering temperature adopted in this work is 850 °C, which is much lower than the melting point of Ag (961 °C), fundamentally suppressing the diffusion behavior of Ag and thus avoiding significant Ag diffusion. In conclusion, this ceramic composition can be co-fired with Ag electrodes for the fabrication of multilayer piezoelectric ceramic devices.

The electrical properties of parallel-connected multilayer thick-film piezoelectric devices based on 0.58PZT–0.1PZN–0.2PNN–0.12PFW ceramics with different numbers of layers are summarized in

Table 1. Electrical properties of 0.58PZT–0.1PZN–0.2PNN–0.12PFW thick films with different layers sintered at 850 °C.

Layers	ε33T/ε0	tan δ	d33 (pC·N−1)	Pr (μC·cm−2)	Ec (kV·cm−1)	g33 (mV·m/N)
1	938	0.0203	176	-	-	21.2
5	875	0.0241	850	28.8	11.0	109.5
7	851	0.0253	1180	45.0	10.9	156.0
9	820	0.0263	1470	72.6	11.1	203.7

. In the parallel configuration, each ceramic layer can generate charge independently under external excitation, resulting in d₃₃ and P_r values that are proportional to the number of layers. The 9-layered sample achieves a d₃₃ value as high as 1470 pC/N, approximately three times that of the same-composition bulk ceramic, demonstrating that the multilayer structure is an effective strategy to obtain high piezoelectric response. Even the single-layer thick film sintered at a low temperature of 850 °C still exhibits a d₃₃ value of 176 pC/N. Furthermore, the relative permittivity ε₃₃^T/ε₀ of the multilayer samples decreases with increasing layer number, accompanied by a slight increase in dielectric loss tanδ, which is attributed to the pore structure formed by the burnout of organic binders and additives during sintering.

Figure 9a shows the P–E hysteresis loops of the multilayer thick films with different layer numbers and the bulk ceramic sintered at 850 °C. All curves of multilayer samples exhibit an asymmetric shape accompanied by an internal bias field. Defect dipoles are inevitably generated during the formation of the PZT–PZN–PNN–PFW solid solution and the polarization aging process. It has been reported that the reorientation of defect dipoles after aging accounts for the occurrence of such asymmetric P–E loops [30]. Furthermore, the coercive field of the multilayer ceramic films showed no obvious change with the increase in the number of parallel layers, which is because the self-supporting structure relieves the substrate’s constraint on the ceramic films.

Figure 9b presents the unipolar displacement–voltage curves of the 9-layer thick films and the bulk ceramic counterpart. The thickness of the bulk ceramic sample is 2 mm, while that of the optimized 9-layer multilayer device is merely approximately 300 μm. When a driving voltage of 250 V is applied, the displacement of the multilayer thick film reaches the same level as that of the bulk ceramic with the identical formula. As the voltage further increases to 500 V, the multilayer film exhibits a remarkable displacement of about 5.5 μm, corresponding to a large strain of 1.83%. These results clearly verify the feasibility of driving this multilayer piezoelectric device under low operating voltages.

4. Conclusions

This study investigated the effect of PFW doping content on the crystal structure, micromorphology and piezoelectric properties of PZT–PZN–PNN piezoelectric ceramics, with the core objective of screening out the optimal composition that enables low-temperature sintering and is suitable for fabricating piezoelectric actuators with Ag electrodes.

The experimental results demonstrate that PFW doping can effectively reduce the sintering temperature of the ceramic system, lowering that of 0.7PZT–0.1PZN–0.2PNN ceramics from 1200 °C to 850 °C. With the increase in PFW doping content, the porosity of the ceramics decreases significantly and the grains grow gradually, with the sample at x = 0.12 exhibiting the optimal crystallinity. The ceramic with x = 0.12 sintered at 850 °C attains a relative density of 98.2%, along with the optimal piezoelectric and dielectric performance: d₃₃ = 477 pC/N, k_p = 0.68 and tanδ = 0.0154.

Performance tests on the fabricated multilayer piezoelectric devices show that the 9-layer ceramic thick film device achieves a displacement of approximately 3.0 μm under a voltage of 250 V, which matches that of the bulk ceramic driven at 6000 V. When the driving voltage is increased to 500 V, the displacement of the 9-layer device reaches 5.5 μm, corresponding to a large strain of 1.83%. In addition, cross-sectional SEM characterization of the devices confirms no obvious diffusion of Ag electrodes after sintering, indicating that the optimized ceramic composition realizes good low-temperature co-firing compatibility with Ag electrodes. Moreover, high-performance multilayer piezoelectric ceramic devices with the advantage of miniaturization can be fabricated via the self-supporting process using this composition.