Rhombohedral-tetragonal Phase Transition Temperature Research Articles

Enhanced electrocaloric effect in Sr-doped Ba0.85Ca0.15Zr0.1Ti0.9O3 lead-free thin films near room temperature

Ferroelectric thin films with giant room-temperature electrocaloric effect (ECE) could be very useful in design of solid-state refrigeration devices. Here, lead-free Ba0.85Ca0.15-xSrxZr0.1Ti0.9O3 (BCZT-xSr, 0.01 ≤ x ≤ 0.10) thin films are successfully prepared on the substrates (Pt/Ti/SiO2/Si) via sol-gel route, and the effect of the Sr substitution on the structure, electric properties and ECE of the films were investigated. The dielectric analyses show that the rhombohedral-tetragonal phase transition temperature (TR-T) move to a higher temperature and the tetragonal-cubic phase transition temperature (Tm) shift to a lower temperature with increasing Sr content, and finally the TR-T peaks merge into the Tm peaks at room temperature. The BCZT-0.05Sr film presents a giant ECE with ΔT = 27.1 K and ΔS = 30.6 J K−1 kg−1 at 800 kV cm-1 near room temperature (301 K). The giant ΔT benefits from a multiphase coexisting region with successive R-T and T-C phase transition character near room temperature. These results indicate that the lead-free Sr-doped BCZT thin film is an attractive material for application in ECE refrigeration devices.

Water Quenched and Acceptor-Doped Textured Piezoelectric Ceramics for Off-Resonance and On-Resonance Devices.

Piezoelectric materials should simultaneously possess the soft properties (high piezoelectric coefficient, d33 ; high voltage coefficient, g33 ; high electromechanical coupling factor, k) and hard properties (high mechanical quality factor, Qm ; low dielectric loss, tan δ) along with wide operation temperature (e.g., high rhombohedral-tetragonal phase transition temperature Tr-t ) for covering off-resonance (figure of merit (FOM), d33 × g33 ) and on-resonance (FOM, Qm × k2 ) applications. However, achieving hard and soft piezoelectric properties simultaneously along with high transition temperature is quite challenging since these properties are inversely related to each other. Here, through a synergistic design strategy of combining composition/phase selection, crystallographic texturing, defect engineering, and water quenching technique, <001> textured 2mol% MnO2 doped 0.19PIN-0.445PSN-0.365PT ceramics exhibiting giant FOM values of Qm × (227-261) along with high d33 × g33 (28-35 × 10-12 m2 N-1 ), low tan δ (0.3-0.39%) and high Tr-t of 140-190°C, which is far beyond the performance of the state-of-the-art piezoelectric materials, are fabricated. Further, a novel water quenching (WQ) room temperature poling technique, which results in enhanced piezoelectricity of textured MnO2 doped PIN-PSN-PT ceramics, is reported. Based upon the experiments and phase-field modeling, the enhanced piezoelectricity is explained in terms of the quenching-induced rhombohedral phase formation. These findings will have tremendous impact on development of high performance off-resonance and on-resonance piezoelectric devices with high stability.

Effects of Nano-Sized In2O3 on Sintering Behavior and Electrical Properties of 0.28Pb(In1/2Nb1/2)O3-0.40Pb(Mg1/3Nb2/3)O3-0.32PbTiO3 Ceramics

0.28Pb(In1/2Nb1/2)O3-0.40Pb(Mg1/3Nb2/3)O3-0.32PbTiO3 ceramics were synthesized by conventional solid-phase method using nano-sized In2O3. All the sintered 0.28PIN-0.40PMN-0.32PT ceramics have pure perovskite structure with composition locating at rhombohedral side around the morphotropic phase boundary (MPB) region. The 0.28PIN-0.40PMN-0.32PT ceramics belong to displacive driving ferroelectrics with apparent diffused phase transition characteristic. Although the rhombohedral-tetragonal ferroelectric phase transition temperature (TR-T) increases only to ∼120 °C due to the solid solution of Pb(In1/2Nb1/2) (PIN), the 0.28PIN-0.40PMN-0.32PT ceramics present high piezoelectric thermal stability till around the Curie temperature (Tm), which extremely widens the working temperature range and makes the 0.28PIN-0.40PMN-0.32PT ceramics suitable for high-temperature piezoelectric applications.

Electrical and magnetodielectric coupling properties of Co-doped PMN-32PT ferroelectric single crystal

Co-doped Pb(Mg1/3Nb2/3)O3–32PbTiO3 (Co-doped PMN–32PT) single crystals were grown by a flux method. The phase structure, dielectric, piezoelectric, ferroelectric and magnetodielectric coupling properties of the crystals were characterized. The result of X-ray diffraction showed Co-doped PMN-32PT single crystal was perovskite phase. The dielectric properties of the Co-doped PMN-32PT single crystal along [001]-orientation has a higher rhombohedral-tetragonal phase transition temperature (Trt~107 °C) and larger coercive field (EC~7.91 kV/cm) than the [001] oriented PMN-32PT single crystal. The piezoelectric constant d33 is 1200 pC/N. Meanwhile, Under the external magnetic field, Co-doped PMN-32PT single crystal has negative magnetodielectric coupling effect.

New strategy to solve temperature sensitivity in (K, Na)NbO3: Modified slope of R-T phase boundary through phase content regulation

The temperature stability of potassium sodium niobate based materials has become a huge challenge due to its polymorphic phase boundary. How to thoroughly solve temperature sensitivity is one of the urgent aims in practical applications. Here, a new strategy of modifying R-T slope through phase content regulation has been achieved in lead-free ceramics of 0.96K0.5Na0.5Nb0.955Sb0.045O3–0.04[(1-x)Bi0.5Na0.5ZrO3-xBi0.5Na0.5SnO3] (0 ≤ x ≤ 0.20) aiming to verify the relationship between phase content and temperature insensitivity. The temperature dependent on Suni, d33, and domain has proved that decreasing of tetragonal (T) phase content as rising rhombohedral-tetragonal phase transition temperature (TR-T) results in poor temperature stability. Moreover, an ideal R-T phase boundary similar to MPB model based on the results is proposed to possibly solve the fundamental problem of temperature sensitivity via increasing T phase content to modify the slope of R-T phase boundary. Therefore, it can be inferred that a more favorable temperature insensitivity can be obtained if one can construct a more slope R-T phase boundary, providing a new thought to consider how to thoroughly solve temperature sensitivity in KNN-based ceramics.

High-field electrostatic control of ferromagnetic resonance in NiFe/PIN-PMN-PT multiferroic heterostructures

We report electric-field control of ferromagnetic resonance in NiFe film, which was deposited on (011)-cut 0.3Pb(In1/2Nb1/2)O3-0.4Pb(Mg1/3Nb2/3)O3-0.3PbTiO3 (PIN-PMN-PT) single crystals. An upward frequency shift from 11.69 to 12.53 GHz is achieved in our heterostructures for electric field from 0 to 15 kV/cm as an external magnetic field of 2090 Oe was applied along in-plane [100] direction, and a downward shift from 13.61 to 13.25 GHz is investigated for electric field from 0 to 7 kV/cm, while an external magnetic field of 2723 Oe was applied along [01$$\stackrel{-}{1}$$] direction. The large operational electric field and the high rhombohedral-tetragonal phase transition temperature TR−T (~ 127 °C) of the crystal make NiFe/PIN-PMN-PT composites great candidates for electrically tunable microwave magnetic device applications with broad electric field and temperature range.

Surface acoustic wave properties in 0.955Pb(Zn1/3Nb2/3)O3-0.045PbTiO3 multidomain single crystal poled along [001

ABSTRACTSurface acoustic wave propagation in a 0.955Pb (Zn1/3Nb2/3)O3-0.045PbTiO3 multidomain single crystal poled along [001]c has been analyzed theoretically using Christoffel wave equations. From the measured experimental data, the orientational dependence of surface acoustic wave phase velocities, electromechanical coupling coefficients and power flow angles was calculated. The results showed that surface acoustic wave propagations of 0.955Pb (Zn1/3Nb2/3)O3-0.045PbTiO3 are poor than 0.93Pb(Zn1/3Nb2/3)O3-0.07PbTiO3 crystal slightly. However, the 0.955Pb (Zn1/3Nb2/3)O3-0.045PbTiO3 single crystals have higher rhombohedral-tetragonal phase transition temperature and much stabler electromechanical properties. This may expand applications range of SAW devices.

Study of temperature-induced structural evolution in (Na0.5Bi0.5)TiO3-(K0.5Bi0.5)TiO3-(K0.5Na0.5)NbO3 lead-free ceramics

In this work, the temperature-induced structural evolution in 0.79(Na0.5Bi0.5)TiO3-0.2(K0.5Bi0.5)TiO3-0.01(K0.5Na0.5)NbO3 (NKBNT) lead-free ceramics was investigated by Raman microscopic spectroscopy combined with electrical macroscopic measurements. The NKBNT ceramics possess the local structure with the coexisted rhombohedral R3c and tetragonal P4bm polar-nano-regions (PNRs). The R3c and P4bm PNRs coexist in a wide temperature range, then the local structure transforms to the P4bm PNRs around the temperature of dielectric maximum (Tm) evidenced by the doublet splitting of Ti-O modes (peak B) and oxygen octahedral vibrational modes (peak C). The discontinuous changes of wavenumber and line-width of peak B2 and peak C3 as well as the dielectric local maxima around the rhombohedral-tetragonal phase transition temperature (TRT) are considered to result from the thermal evolution of R3c and P4bm PNRs. The macroscopic changes of non-polar phase with electric field and temperature were investigated by the temperature-dependent polarization-electric field (P-E) loops, current-electric field (I-E) loops and bipolar strain (S-E) curves. The electric-field level necessary to form the long-range ferroelectric order from non-polar phase associated with the stability of the induced ferroelectric phase depends strongly on the temperature.

Effects of Cr2O3 doping on the microstructure and electrical properties of (Ba,Ca)(Zr,Ti)O3 lead-free ceramics

Lead-free ceramics (Ba0.85Ca0.15)(Zr0.1Ti0.9)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 Cr5 + 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.

Growth and characterization of Pb(Lu1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3 ternary piezo-/ferroelectric crystals

Piezo-/ferroelectric crystals of Pb(Lu1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3 ternary solid solution system with high Curie temperature, in the vicinity of morphotropic phase boundary (MPB) region, are grown by the top-seeded solution growth (TSSG) method for the first time. The compositions and structures of the crystals are analyzed, all the structures are found to have pure perovskite structure using X-ray diffraction analysis. Di-/piezo-/ferroelectric properties of the crystals are also characterized systematically. The Curie temperature Tc and coercive field Ec, increase gradually with increasing PbTiO3 content. In particular, the crystal with composition 0.34PLN-0.31PMN-0.35PT possesses excellent electric properties including the Curie temperature, the rhombohedral–tetragonal phase transition temperature, the piezoelectric coefficient, the remnant polarization and the coercive field, which are Tc = 228 °C, TRT = 156 °C, d33 = 2092 pC N−1, Pr = 35.5 μC cm−2 and Ec = 8.1 kV cm−1, respectively, making it a promising material for transducers or detectors in a wide temperature range.

Structural and electrical properties of Ho3+-modified Pb(Zn1/3Nb2/3)O3–9PbTiO3 single crystals

Ho3+-modified Pb(Zn1/3Nb2/3)O3–9PbTiO3 (PZN–9PT) single crystals were grown through a flux method. Phase structure and microstructural morphology of the as-grown single crystals were performed by X-ray diffraction analysis and scanning electron microscopy. The refinement of the lattice parameters were obtained by the Rietveld method. The electrical properties of PZN–9PT single crystals were improved significantly by the modification of Ho3+ ions. The rhombohedral–tetragonal phase transition temperature, Curie temperature, coercive field at 15 kV cm−1, and remnant polarization of Ho3+-modified PZN–9PT single crystals were increased by 14, 42 K, 2.4 kV cm−1, and 7.5 μC cm−2, respectively (i.e., 375.45, 448.45 K, 5.9 kV cm−1, and 38.40 μC cm−2, respectively). Furthermore, Lorentz-type law was used to describe the dielectric relaxor behavior of the as-grown single crystals.

Structural, dielectric and ferroelectric properties of lead-free Na0.5Bi0.5TiO3 ceramics prepared by spark plasma sintering technique

Lead-free Na0.5Bi0.5TiO3 (NBT) fine-grained ceramics were prepared by spark plasma sintering method. Single phase ceramics with an ABO3 perovskite structure were confirmed by X-ray diffraction method. The grain morphology was analyzed by using a scanning electron micrograph. The crystal particles arranged compactly and the typical grain size was about ≈200 nm. The depolarization temperature T d, the rhombohedral–tetragonal phase transition temperature T R−T and the temperature T m of the maximum dielectric constant corresponding to tetragonal–cubic phase transition were determined to be 453 K, approximately 623 and 793 K, respectively, from the temperature dependence of dielectric properties. The P-E hysteresis loop at different temperatures indicated the existence of antiferroelectric state at the depolarization temperature T d, which explained the antiferroelectric phase above T d. The values of P s, P r and E c reduced slightly with increasing temperature in the range 303–453 K.

Growth and characterization of high-Curie temperature Pb(Lu1/2Nb1/2)O3–Pb(Mg1/3Nb2/3)O3–PbTiO3 ternary single crystal by modified Bridgman technique

A new relaxor-based ferroelectric ternary system Pb(Lu1/2Nb1/2)O3–Pb(Mg1/3Nb2/3)O3–PbTiO3 (PLN–PMN–PT), with a combination of a high-Curie temperature system Pb(Lu1/2Nb1/2)O3–PbTiO3 (PLN–PT) and a high piezoelectricity system Pb(Mg1/3Nb2/3)O3–PbTiO3 (PMN–PT), was investigated in this paper. Single crystal PLN–PMN–PT with dimensions of Φ20×45mm3 was grown successfully by the modified Bridgman technique for the first time. The studies of structure and composition of the as-grown crystal showed structural consistency but compositional deviation along the growth direction. The 〈001〉-oriented wafers of the PLN–PMN–PT single crystal showed excellent electrical properties at room temperature: ε33~4500, tanδ~0.5%, d33~2300pC/N. The crystal was found to exhibit high Curie temperature (TC~176°C), rhombohedral–tetragonal phase transition temperature (TRT~108°C) and coercive field (EC~8.1kV/cm), superior to those of PMN–0.3PT single crystal. Studies of temperature dependence ferroelectric properties showed that high values of k33 and d33 could be maintained up to the TRT. These results showed that PLN–PMN–PT piezoelectric single crystal has a higher Curie temperature and coercive field with excellent electrical properties, making the crystal a promising candidate for high-power transducer applications in a broad temperature range.

Phase transitional behavior and electrical properties of Pb(In1/2Nb1/2)O3–Pb(Mg1/3Nb2/3)O3–PbTiO3 ternary ceramics

Relaxor based ternary (0.60 − x)Pb(In1/2Nb1/2)O3–0.40Pb(Mg1/3Nb2/3)–xPbTiO3 ((0.60 − x)PIN–0.40PMN–xPT) polycrystalline ceramics were synthesized by two-step columbite precursor method. The effects of PIN/PT content on phase structure, microstructure, density, and dielectric, piezoelectric, ferroelectric and pyroelectric properties of the ternary ceramics were systematically investigated. A morphotropic phase boundary (MPB) near x = 0.34 was identified by X-ray diffraction and further confirmed by their respective electrical properties. Piezoelectric, ferroelectric and pyroelectric properties were enhanced for compositions near the MPB. The 0.26PIN–0.40PMN–0.34PT ceramics show optimum electrical properties: piezoelectric coefficient d 33 = 505 pC/N, planar electromechanical coupling factor k p = 62.5 %, remnant polarization P r = 32.1 μC/cm2, coercive field E c = 8.8 kV/cm, and room temperature pyroelectric coefficient p = 0.050 μC/cm2 °C. In addition, the rhombohedral–tetragonal phase transition temperature T rt and Curie temperature T c of the ternary ceramics were identified by the temperature dependence of dielectric and pyroelectric measurements, which are much higher than those of binary PMN–PT ceramics, indicating the expanded temperature usage range of the ternary ceramics. The results show that this ternary system is a promising candidate for electromechanical applications with high performance and wide temperature usage range.

High piezoelectric response of a new ternary ferroelectric pb(Ho1/2Nb1/2)O3-pb(Mg1/3Nb2/3)O3-PbTiO3 single crystal

A ternary piezo-/ferroelectric crystal of Pb(Ho1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3 with dimensions of 24×24×15mm3 has been grown by the top-seeded solution growth (TSSG) method for the first time. The structural and the di-/piezo-/ferro-electric properties of the grown crystal were characterized. The piezoelectric coefficient d33 reaches 3297 pC/N in [001]-oriented sample, much higher than the other previously reported ternary crystals. The Curie temperature TC and the rhombohedral-tetragonal phase transition temperature TRT reaches 140°C and 76°C, respectively. The dielectric constant ε΄, dielectric loss tangent tanδ, longitudinal electromechanical coupling coefficient k33, remnant polarization Pr and coercive field Ec at room temperature for [001]-oriented crystals were found to be 10390, 0.068, 92%, 24.5µC/cm2 and 3.22kV/cm, respectively. These results show that the Pb(Ho1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3 crystal is a promising candidate for the application in electromechanical transducers field.

Flux growth and effect of cobalt doping on dielectric, conductivity and relaxation behaviour of 0.91Pb[Zn1/3Nb2/3]O3–0.09PbTiO3crystals

Crystals of 1 mol% cobalt-doped Pb(Zn1/3Nb2/3)O3–0.09PbTiO3 (PZNCT) have been grown using a high-temperature self-flux method. A pure perovskite phase with mixed symmetry at room temperature was observed using X-ray diffraction analysis. Their electrical properties were further investigated by measuring temperature- and frequency-dependent dielectric constant (e) and loss (tan δ) behaviour of as-grown crystals. To study the degree of dielectric relaxation, modified power law fitting and Lorentz-type quadratic fitting were performed. The as-grown PZNCT crystals showed a low Curie temperature (Tc ~131 °C) with a rhombohedral–tetragonal phase transition temperature (Trt) of 104 °C. The piezoelectric coefficient (d33) value at the optimized poling field was found to be ~1000 pC N−1. Complete electrical characterization revealed the growth of high-performance PZNCT crystals with enhanced remnant polarization (34.23 μC cm−2) and low coercive field (6.97 kV cm−1) with cobalt doping. The conduction and relaxation mechanisms of grown PZNCT crystals have been discussed in detail.

Growth and Characterization of a New Lead Lutetium Niobate with Lead Ti-tanate Ferroelectric Crystal

A series of new lead lutetium niobate with lead titanate (1-x)Pb(Lu1/2Nb1/2)O3-xPbTiO3 (PLN-xPT) ferroelec- tric crystals were grown successfully by the top-seed solution growth technique. Structural analysis and electrical proper- ties measurement showed that the crystals have high Curie temperatures and each composition had different performances. The temperature dependences of permittivity showed typical relaxor behavior in the rhombohedral phase region. Based on the measurement result, a solid state phase diagram in the low temperature range was established, which revealed a mor- photropic phase boundary (MPB) in the composition of x = 0.49 to 0.51. Electric domains on (001) surface were observed by the polarizing microscope, in agreement with the X-ray diffraction data. Those compositions within MPB exhibited good piezoelectric properties, such as high coercive field Ec (>10 kV/cm) and high rhombohedral-tetragonal phase transition temperature TRT (> 200 ℃). For PLN-0.49PT, it had a high Curie temperature Tc = 360 ℃ and a piezoelectric coefficient of d33 > 1600 pC/N. High Curie temperature and excellent piezoelectric property make this material a promising candidate

The growth status of relaxor-based ferroelectric crystals and their development trends

Our progress in the growth of ternary system Pb ( In 1/2 Nb 1/2) O 3– Pb ( Mg 1/3 Nb 2/3) O 3– PbTiO 3 (PIMNT) crystals and reviews on the possible developing trends in the piezoelectric crystals are presented. Large PIMNT crystals with 3 inches in diameter have been grown by using a modified Bridgman method. Meanwhile, Mn -doped PIMNT crystals have also been obtained. PIMNT crystals exhibit Curie temperature Tc ~ 190° C , rhombohedral–tetragonal phase transition temperature T rt &gt; 100° C and coercive field Ec ~ 5.0–7.0 kV/cm on (001) cuts. Meanwhile, higher piezoelectric constant d32 ~ -1500–2200 pC/N , d15 ~ 4000–6000 pC/N and coercive field Ec ~ 7.0–9.0 kV/cm have been achieved on (110) cuts. The development trends of relaxor-based ferroelectric crystals are suggested to grow novel crystals with high rhombohedral–tetragonal phase transition temperature T rt &gt; 150 ~ 160° C and/or high coercive field Ec and mechanical quality factor Qm, to promote growth efficiency of PIMNT crystals and to create new growth methods fitting for the growth of metastable or instable crystals.

A new (1 − x)Pb(Lu1/2Nb1/2)O3–xPbTiO3 binary ferroelectric crystal system with high Curie temperature

A series of new (1 − x)Pb(Lu1/2Nb1/2)O3–xPbTiO3 (PLN–xPT) binary ferroelectric crystals with high Curie temperature have been successfully obtained firstly by top-seed solution growth technique. A solid-state phase diagram in the low temperature range has been established based on the form of single crystals, which reveals a morphotropic phase boundary (MPB) in the range of 49–51% PT. The polarized light microscope analysis also confirms the coexistence of rhombohedral and tetragonal phase within the MPB. Furthermore, those compositions within MPB exhibit good comprehensive piezoelectric properties. For example, the crystal with composition PLN–0.49PT, showing high Curie temperature Tc = 360 °C and high rhombohedral–tetragonal phase transition temperature TRT = 110 °C, and the piezoelectric coefficient d33, electromechanical coupling coefficient k33, coercive field Ec and remanent polarization Pr are found to be 1630 pC N−1, 81%, 13.8 kV cm−1 and 26.6 μC cm−2, respectively. The large coercive field and high Tc make it a promising candidate for high power transducers in a wider temperature range.

A Pb(In1/2Nb1/2)O3–Pb(Zn1/3Nb2/3)O3–PbTiO3 ternary ferroelectric system with high TC and high piezoelectric properties

(0.79−x)Pb(In1/2Nb1/2)O3–0.21Pb(Zn1/3Nb2/3)O3–xPbTiO3 (x=0.23–0.35) ternary ferroelectric system in the form of ceramics have been synthesized. Its structure and properties have been studied by X-ray powder diffraction and electric measurements. A morphotropic phase boundary region has been determined in the composition range of 0.28<x<0.32, where the Curie temperature TC and the rhombohedral–tetragonal phase transition temperature TRT were found to vary from 243°C to 295°C and 145°C to 191°C, respectively, much higher than PMNT and PZNT systems. The compositions within MPB region exhibit excellent piezoelectric properties such as piezoelectric coefficient d33>646pC/N, TRT>145°C, TC>273°C and EC>13kV/cm for 0.5PIN–0.21PZN–0.29PT and 0.49PIN–0.21PZN–0.30PT, making the ceramics of this system a promising material for high power and high temperature application.