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The dielectric and pyroelectric performances of 91.5[Formula: see text][Formula: see text]TiO3–8.5[Formula: see text][Formula: see text]TiO3 lead-free single crystal were investigated. The depolarization temperature of the crystal is about 153 [Formula: see text]C. Among the , , and crystallographic orientations, the -oriented crystal possesses the highest pyroelectric coefficient and the largest figures of merit, and the values of [Formula: see text], [Formula: see text], and [Formula: see text]are 5.63×10[Formula: see text] C/m2 •K, 0.06 m2/C, and 21.5 [Formula: see text]Pa[Formula: see text] for the -oriented crystal at room temperature. The [Formula: see text]and [Formula: see text]exhibit weak frequency dependence in the range of 100–300 Hz. With the increase of the temperature, the value of [Formula: see text]increases, while the value of [Formula: see text] decreases from 18 [Formula: see text]C to 103 [Formula: see text]C.

Gd 1-x Ho x Ni melt-spun ribbons were fabricated by a single-roller melt spinning method. All the compounds crystallize in an orthorhombic CrB -type structure. The Curie temperature ( T C ) was tuned between 46 and 99 K by varying the concentration of Gd and Ho. A spin reorientation ( SRO ) transition is observed around 13 K. Different from T C , the SRO transition temperature is almost invariable for all compounds. Two peaks of magnetic entropy change (Δ S M ) were found. One at the higher temperature range was originated from the paramagnet-ferromagnet phase transition and the other at the lower temperature range was caused by the SRO transition. The maximum of Δ S M around T C is almost same. The other maximum of ΔS M around SRO transition, however, had significantly positive relationship with x. It reached a maximum about 8.2 J kg −1 K −1 for x = 0.8. Thus double large Δ S M peaks were obtained in Gd 1-x Ho x Ni melt-spun ribbons with the high Ho concentration. And the refrigerant capacity power reached a maximum of 622 J kg −1 for x = 0.6. Gd 1-x Ho x Ni ribbons could be good candidate for magnetic refrigerant working in the low temperature especially near the liquid nitrogen temperature range.

A series of NBT-KBT lead-free crystals with dimensions of Φ 35×10 mm were successfully grown by the TSSG method. The as-grown crystals possess rhombohedral perovskite structure at room temperature. The curves e(T) for all crystals show two abnormal dielectric peaks. The depolarization temperatures Td derived from the first peak of curves tan δ(T) vary with the KBT content, which are 130, 150, 140, and 115 °C respectively, for (100−x)NBT−xKBT (x=5, 8, 12, 15) crystals, being well consistent with the Td obtained from the temperature dependence of kt. A notable thermal hysteresis, ΔT≈35 °C, for ferroelectric-antiferroelectric phase transition was also disclosed for 92NBT-8KBT crystal. The investigation of orientation dependence for electrical properties disclosed the dielectric parameters show weak anisotropy. The piezoelectric constants (d33) are 147, 175, 205, 238 pC/N and the values of kt are 38%, 52%, 52%, 54%, respectively for (100−x)NBT−xKBT (x=5, 8, 12, 15) crystals.

Magnetocaloric effect and critical behavior of amorphous ribbons Gd54Ho6Co25Al14Si were investigated in this paper. Samples were fabricated by a single-roller melt-spinning method at a spinning rate of 20 and 60 m/s. The Curie temperature is 120 K for both samples. A broader phase transition temperature range, however, was found for the sample fabricated at 60 m/s. It was attributed to its higher local disordered structure due to its faster quenching speed. The peak of the magnetic entropy change $\Delta S^{\textrm {PK}}_{M}$ is 11.01 $\text{J}\,\cdot \,$ kg $^{-1}\cdot \text{K}^{-1}$ and its full-width of the half-maximum is $\sim 90$ K at a field change of 0–5 T, which results in a large refrigerant capacity ( $\sim 990$ J $\cdot $ kg $^{-1}$ ).

Magnetocaloric effect and critical behavior of Ni2In-type compound FeMn1−xNixGe were investigated in the present work. By partial substitution of Ni for Mn in FeMnGe, the magnetic transition temperature (TC) is tuned in a wide temperature range between 160 and 320 K with x (Ni concentration) varying from 0 to 0.4. A ferromagnet (FM) to paramagnet (PM) magnetic phase transition is observed and the magnetization has a sharp drop around respective phase transition temperature for all the compounds. The maximum magnetic entropy change is found to be 3.9 J/kg K and 4.1 J/kg K for a 5 T field change with x = 0.2 and 0.3, respectively, making them a promising candidate for magnetic refrigeration near room temperature. To investigate the nature of PM–FM phase transition, the critical behavior near TC was analyzed based on the Arrott plots. The critical values obtained with the conventional Arrott-plot procedure are very close to those predicated by the mean-field model. This suggests a long-range exchange interaction and a second order magnetic phase transition in FeMn1−xNixGe.

A large-size 0.88Na0.5Bi0.5TiO3–0.12K0.5Bi0.5TiO3 lead-free piezoelectric single crystal with dimensions of ∅30 mm ×10 mm was successfully grown by the top-seeded solution growth method. X-ray powder diffraction measurement showed that the as-grown crystal possesses a rhombohedral perovskite structure at room temperature. The temperature dependence of dielectric constant and loss, polarization hysteresis loop, electric-field-induced strain, and the electromechanical coupling property were investigated for the -oriented as-grown crystal. The remanent polarization P r, the piezoelectric constant d 33, and the electromechanical coupling coefficient k t at room temperature are 13.8 pC/cm2, 205 pC/N, and 51 %, respectively. The maximum strain of 0.23 % was obtained under 30 kV/cm. The temperature dependence of k t demonstrated a relatively stable thermal electromechanical coupling property over the temperature range of 20–150 °C.

0.95Na 0.5 Bi 0.5 TiO 3 –0.05K 0.5 Bi 0.5 TiO 3 lead-free piezoelectric single crystal with rhombohedral structure was grown by the top-seeded solution growth method. The temperature dependence of dielectric constant and loss, polarization hysteresis loops, the optimum poling condition and the electromechanical coupling property were investigated for the 〈100〉-oriented as-grown crystal. The curves e ( T ) show two anomalies, which are related to the two phase transformations at the temperature range of 130–340 °C. The piezoelectric constant d 33 and electromechanical coupling coefficient k t for the 〈001〉-oriented crystal at room temperature reached 147 pC/N and 0.52, respectively. The value of k t demonstrated a relatively stable thermal electromechanical coupling property over the temperature range of 15–130 °C.

The 0.96Na0.5Bi0.5TiO3–0.04K0.5Bi0.5TiO3 (NKBT96/4) lead-free single crystal was successfully grown by top-seeded solution growth method. The effective segregation coefficient for K was calculated to be 0.20. X-ray powder diffraction measurement showed that the as-grown crystal possesses rhombohedral perovskite structure at room temperature. X-ray rock curve measure indicated that the as-grown single crystal owned relatively higher quality. The NKBT96/4 single crystal exhibits apparent diffused dielectric behavior, where the diffusiveness index α is 1.79 for the [001]-oriented crystal planes. A notable thermal hysteresis, ΔT h , of 25°C was disclosed for the tetragonal antiferroelectric-tetragonal paraelectric phase transition in the dielectric property studies between heating and cooling. The highest remnant polarization, P r , 16.8 μC/cm2, was obtained at 100°C. The electromechanical coupling coefficient kt of the [001]-oriented crystal planes at room temperature was determined to be 38% using resonance–antiresonance technique. The room temperature piezoelectric constant d33 reaches 120 pC/N.

Lead-free piezoelectric materials such as Na0.5Bi0.5TiO3-BaTiO3 (NBBT) solid solution have been paid increasing attention from an environmental perspective. In this paper, a series of NBBT single crystals with compositions near the morphotropic phase boundary (MPB) were grown by the top-seeded solution growth (TSSG) method. The compositional dependence of crystalline structure was investigated by high-resolution X-ray diffraction (XRD). In addition, the dielectric, piezoelectric and ferroelectric (FE) properties of NBBT crystals were also investigated. Excellent piezoelectric properties of NBBT crystals, especially large thickness coupling factors kt, were obtained near the MPB, which are more than or close to the performances of PZT ceramics. Moreover, the performances of NBBT crystals can be further enhanced by doping. Finally, the domain configurations of NBBT96/4 crystal were studied preliminarily.

Mn doped 0.95Na0.5Bi0.5TiO3–0.05BaTiO3 (NBBT5) single crystal was grown by the top-seed solution growth (TSSG) method. After different annealing processes, the temperature dependence of conductivity and Arrhenius relation were used to calculate the conduction activation energies and analyze the defect structure in Mn:NBBT5 crystal. Two different activation energies in different temperature regions were observed, corresponding to different conduction mechanisms. It should be noted that a large electro-strain up to 1% was obtained after being annealed in oxygen atmosphere, due to the “aged effect”.

(1− x )(Ni 0.8 Zn 0.1 Cu 0.1 )Fe 2 O 4 /x0.58Pb(Ni 1/3 Nb 2/3 )O 3 -0.02Pb(Zn 1/3 Nb 2/3 )O 3 -0.05Pb(Ni 1/2 W 1/2 )O 3 -0.35PbTiO 3 ((1− x )NZCF/xPNZNWT) magnetoelectric composites were prepared by conventional solid–state reaction method via low-temperature sintering technique. The low-temperature sintering technique can prepare dense composites, where the ferrite and piezoelectric phases coexist in the synthesized particulate composites, and no apparent mutual solubility takes place between the two phases. The (1− x )NZCF/xPNZNWT ceramic composites exhibit excellent integrated electrical properties, where diffused dielectric response peaks, typical P-E hysteresis loops and excellent piezoelectric property can be obtained. The (1− x )NZCF/xPNZNWT composites prepared by the low-temperature sintering process can be electrically and magnetically poled to exhibit apparent magnetoelectric effect, indicating that such technique is convenient to develop excellent particulate magnetoelectric materials in the future.

Mn-doped 0.948Na0.5Bi0.5TiO3–0.052BaTiO3 (NBBT94.8/5.2) lead-free single crystal with excellent piezoelectric and electromechanical coupling properties was successfully grown by top-seeded solution growth method (TSSG). X-ray powder diffraction measurement showed that the as-grown crystal possesses rhombohedral perovskite structure. The Mn-doped NBBT94.8/5.2 single crystal exhibits apparent diffused dielectric behavior, in which the diffusiveness index α is 1.99 for the [001]-oriented crystal planes. A notable thermal hysteresis is disclosed for the rhombohedral-tetragonal phase transition between heating and cooling studies in the dielectric property. The electromechanical coupling coefficients of Mn-doped NBBT94.8/5.2 were determined experimentally using the resonance–antiresonance technique. The room-temperature electromechanical coupling coefficients k 31, k 31〈110〉, k 33, k t are 35.9%, 35.5%, 68.5%, 58.7%, respectively. The room-temperature piezoelectric constants d 33, d 31 reach as high as 457, 138 pC/N respectively. The value of k t increases slightly with the increase of temperature from −80 to 70°C, demonstrating a relatively stable thermal electromechanical coupling property.

A total of 5 mol% WO3-doped (1−x)(Ni0.8Zn0.1Cu0.1)Fe2O4/xPb(Ni1/3Nb2/3)O3–Pb(Zn1/3Nb2/3)O3–PbTiO3 ((1−x)NZCF/xPNN-PZN-PT) magnetoelectric particulate ceramic composites were prepared by conventional solid-state reaction method via low-temperature sintering process. X-ray diffraction (XRD) measurement and scanning electron microscopy (SEM) observation indicate that piezoelectric phase and ferrite phase coexist in the sintered particulate ceramic composites. Dielectric property of the (1−x)NZCF/x0.53PNN–0.02PZN–0.05Pb(Ni1/2W1/2)O3–0.40PT ((1−x)NZCF/xPNN-PZN-PNW-PT, nominal composition) composites is improved greatly as compared to that of the undoped (1−x)NZCF/xPNN-PZN-PT composites. The WO3-doped (1−x)NZCF/xPNN-PZN-PT composites exhibit typical P–E hysteresis loops at room temperature accompanied by the decrease of saturation polarization (Ps) and remnant polarization (Pr). At the same time, piezoelectric property of the composites deteriorates greatly with the increase of ferrite content. The (1−x)NZCF/xPNN-PZN-PNW-PT composites can be electrically and magnetically poled and exhibit apparent magnetoelectric (ME) effect. A maximum ME voltage coefficient of 13.1 mV/(cm Oe) is obtained in the 0.1NZCF/0.9PNN-PZN-PNW-PT composite at 400 Oe d.c. magnetic bias field superimposed 1 kHz a.c. magnetic field with 5 Oe amplitude. The addition of WO3 in the piezoelectric phase decreases sintering temperature greatly from 1180 °C to 950 °C and decreases dielectric loss sharply of the composites, thus the ME voltage coefficient increases. Such ceramic processing is valuable for the preparation of magnetoelectric particulate ceramic composites with excellent ME effect.

Phase pure perovskite (1− x − y )Pb(Ni 1/3 Nb 2/3 )O 3 – x Pb(Zn 1/3 Nb 2/3 )O 3 – y PbTiO 3 (PNN–PZN–PT) ferroelectric ceramics were prepared by conventional solid-state reaction method via a B-site oxide mixing route. The PNN–PZN–PT ceramics sintered at the optimized condition of 1185 °C for 2 h exhibit high relative density and rather homogenous microstructure. With the increase of PbTiO 3 (PT) content, crystal structure and electrical properties of the synthesized PNN–PZN–PT ceramics exhibit successive phase transformation. A morphotropic phase boundary (MPB) is supposed to form in (0.9− x )PNN–0.1PZN– x PT at a region of x =32–36 mol% confirmed by X-ray diffraction (XRD) measurement and dielectric measurement. The MPB composition can be pictured as providing a “bridge” connecting rhombohedral ferroelectric (FE) phase and tetragonal one since crystal structure of the MPB composition is similar to both the rhombohedral and tetragonal lattices. Dielectric response of the sintered PNN–PZN–PT ceramics also exhibits successive phase-transition character. 0.64PNN–0.1PZN–0.26PT exhibits broad, diffused and frequency dependent dielectric peaks indicating a character of diffused FE–paraelectric (PE) phase transition of relaxor ferroelectrics and 0.40PNN–0.1PZN–0.50PT exhibits narrow, sharp and frequency independent dielectric peaks indicating a character of first-order FE–PE phase transition of normal ferroelectrics. The FE–PE phase transition of 0.56PNN–0.1PZN–0.34PT is nearly first-order with some diffused character, which also exhibits the largest value of piezoelectric constant d 33 of 462pC/N.

(1 − x )Sr(Fe 1/2 Nb 1/2 )O 3 – x PbTiO 3 (SFN–PT) ferroelectric ceramics were prepared by conventional solid-state reaction method via the wolframite precursor route. X-ray diffraction (XRD) measurement confirmed that the synthesized SFN–PT ceramics are of pure perovskite structure. With the increase of the concentration of PbTiO 3 (PT), crystal structure of the sintered SFN–PT ceramics changes from rhombohedral phase to tetragonal phase. Dielectric response of the SFN–PT ceramics changes from diffused and broad dielectric peaks to relatively sharp ones accompanied by the increase of the temperature of dielectric maximum ( T m ). Small content of MnO 2 or Li 2 CO 3 doping can greatly decrease the dielectric loss of the SFN–PT ceramics, furthermore, the abnormal increase of dielectric constant and loss tangent in the paraelectric phase is suppressed accordingly. Typical P-E hysteresis loops are observed in the SFN–PT ceramics, however, the saturate polarization ( P s ) is small. MnO 2 or Li 2 CO 3 doping can greatly decrease the coercive field ( E c ) of the SFN–PT ceramics accompanied by large increase of P s . Piezoelectric constant d 33 of the SFN–PT ceramics is small except for SFN30–PT70 ceramics, which reaches 22pC/N.

Pb(Fe1/2Nb1/2)O3 (PFN) ferroelectric ceramics with pure perovskite structure were synthesized successfully by conventional solid-state reaction method via the direct calcining route and the wolframite precursor route. The feasible formation of pure perovskite phase PFN can be attributed to its appropriate tolerance factor and electronegativity difference. PFN ceramics prepared by the above both methods exhibit broad dielectric response peaks (ϵm) accompanied by large dielectric loss and apparent dielectric frequency dispersion, with temperatures of dielectric maximum (Tm) locating at around 90 °C. 0.25 wt% MnO2 and 0.25 wt% Li2CO3 doping can greatly decrease dielectric loss and sharpen dielectric response peaks of the PFN ceramics synthesized by the above both methods. The dielectric frequency dispersion is also suppressed accordingly. However, Tm of the MnO2- and Li2CO3-doped PFN ceramics maintains almost invariable. The remanent polarization (Pr) of the MnO2- and Li2CO3-doped PFN ceramics prepared by the wolframite precursor method is slightly larger than Pr of those prepared by the direct calcining method. Piezoelectric constant d33 of the 0.25 wt% MnO2-doped PFN ceramics prepared by the direct calcining method is the largest among all the samples synthesized, reaching 134 pC/N. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Several relaxor-based complex perovskite ferroelectric ceramics were synthesized by conventional solid-state reaction method via different routes, i.e., the B-site oxide mixing route, the straight calcination method and the columbite/wolframite precursor method. Structure analysis and physical properties measurements prove that the B-site oxide mixing route is efficient and feasible in the synthesizing of complex perovskite ferroelectrics since such a technique is superior in suppressing pyrochlore phases, stabilizing the perovskite structure, and improving the amount of perovskite phase as compared to the straight calcination method and the columbite/wolframite precursor method. The dielectric properties are improved correspondingly, namely exhibiting the largest value of dielectric maximum, the sharpest dielectric response peaks and the least frequency dispersion of dielectric properties in the ferroelectric ceramics prepared via the B-site oxide mixing route, which is considered as correlating with the amount of pyrochlore phases, ceramic density, grain size, and microstructure morphology of the ceramics synthesized.

It has been found that rare earth based metallic glasses manifested large magetocaloric effect over much wider temperature range than most of the crystalline materials. It was mainly attributed to their unique microstructure-a long range disorder and a short range order. In this work, we investigated the magnetocaloric effect in Gd 54 Ho 6 Co 25 Al 14 Si amorphous ribbons. A large magnetic entropy change and a relative high refrigerant capacity were observed. The critical behavior was studied near the phase transition temperature.

We investigated the pyroelectric properties of ⟨001⟩, ⟨110⟩, and ⟨111⟩-oriented Mn doped 94.6Na0.5Bi0.5TiO3-5.4BaTiO3 (94.6NBT-5.4BT) crystals. Among the above three crystallographic orientations, the ⟨111⟩-oriented crystals possess the highest pyroelectric coefficients and the largest figures of merit. At 20 °C, the values of p, Fv, and Fd reach as high as 5.88 × 10−4 C/m2 K, 29.8 μPa−1/2, and 0.08 m2/C for ⟨111⟩-oriented crystals, respectively, which are superior to other lead-free ferroelectric materials. The crystals also demonstrate a high depolarization temperature and relatively stable thermal pyroelectric property. These results indicate the potential of Mn-doped 94.6NBT-5.4BT crystals for lead-free infrared pyroelectric detectors.

(1 − x)(Ni0.8Zn0.1Cu0.1)Fe2O4/x0.48Pb(Ni1/3Nb2/3)O3–0.02Pb(Zn1/3Nb2/3)O3–0.05Pb(Ni1/2W1/2)O3–0.45PbTiO3 ((1 − x)NZCF/xPNZNWT) magnetoelectric particulate ceramic composites were prepared by the conventional solid-state reaction method via a low-temperature sintering process. X-ray diffraction (XRD) measurements and scanning electron microscopy (SEM) observation confirm that ferrite and piezoelectric phases coexist in the sintered particulate composites. With the addition of sintering aids, densified ceramic composites can be prepared by the low-temperature sintering technique, which can improve the dielectric properties of the synthesized (1 − x)NZCF/xPNZNWT composites. The (1 − x)NZCF/xPNZNWT composites exhibit typical P–E hysteresis loops, where remnant polarization Pr decreases and coercive field Ec increases accompanied by the decrease of piezoelectric constant d33 with the increase of the ferrite phase incorporated into the composites. Although a magnetoelectric (ME) voltage coefficient of just 7.34 mV (cm Oe) − 1 is obtained in the 0.2NZCF/0.8PNZNWT composite, it is expected to be comparable to that of the reported bulk composites when the magnitude of the ac magnetic field increases and the frequency of the ac magnetic field increases to the resonant frequency of the piezoelectric phase.