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Lead-free has been a goal that people pursue due to the environmental pollution caused by lead in lead-based materials. K0.5Na0.5NbO3(KNN) is one of the most promising lead-free piezoelectric materials. Theoretically, the piezoelectric properties of single crystals are much better than those of polycrystalline materials. However, it is difficult to fabricate uniform KNN-based crystals by the high-temperature melt method because of volatilization of elements. This method also needs complicated equipment and is expensive. Here, a seed-free, solid-state crystal growth (SFSSCG) method was used to prepare Mn, Li, and Bi co-doped KNN crystals, which show an ultrahigh piezoelectric coefficient of about 1050 pC N−1, around one order of magnitude higher than that of pure KNN ceramics. Furthermore, the effective piezoelectric coefficient d33* of this crystal can reach 2290 pm V−1 at a unipolar electric field of 10 kV cm−1. This crystal also shows a high Curie temperature and good ferroelectricity. It is expected that the lead-free KNN-based single crystals fabricated by this simple method show promise for high performance ferroelectric and piezoelectric applications in industry and are environment-friendly.

In this work, based on a composition design, a pure K0.52Na0.48NbO3 (KNN) lead-free piezoelectric single crystal with a maximum dimension of 4 mm × 4 mm × 2 mm was successfully prepared by the seed-free solid-state crystal growth method. The X-ray diffraction results indicate that the as-grown KNN single crystals have a perovskite crystalline structure with a single orthorhombic phase. An porous microstructure exists in the pure KNN single crystal in this present. The orthorhombic-tetragonal T O−T and tetragonal-cubic phase transition temperature Curie temperature T C of the single crystal are found at 190 and 424 °C, respectively. The obtained KNN single crystal exhibits a piezoelectric coefficient d 33 of 103 pC/N and relative dielectric permittivity ɛ of 180. The resistance of KNN single crystal is insensitive to the temperature in the measurement range. The conductive mechanism of the single crystal mainly comes from the grain interiors.

FePd alloy films with different thicknesses have been prepared by DC magnetron sputtering on glass. The effect of thin film thickness on the structural and magnetic properties was investigated by X-ray diffraction (XRD), energy dispersive spectroscope (EDS), and physical property measurement system. The results indicate that the ordering process in the thin FePd alloy film occurs in the thicker ones. In-plane coercivity value first increases rapidly as thickness increases from d=22.5 to d=67.5 nm, and then the value decreases with further increasing film thickness. A peak value of coercivity 3.2×79.6 kA/m appears at d=67.5 nm.

The influence of minor Pr substitution on the magnetocaloric effect (MCE) of Mn1−x Pr x As (x = 0.005, 0.01, 0.015, 0.02) alloys has been investigated. The lattice parameters a, c and unit cell volume V of the alloys Mn1−x Pr x As (x = 0.005, 0.01, 0.015, 0.02) increase monotonically with increasing Pr content. The Pr addition has minor effect on tuning the Curie temperature T c from 318 K to 321 K for x = 0.005–0.02 and reducing the thermal hysteresis (about 20 K). With increasing the temperature, the critical field induced paramagnetic (PM)–ferromagnetic (FM) transition shifts to higher values. The Pr substitution makes the paramagnetic phase unstable and stabilizes the ferromagnetic phase, which lead to increasing in Curie temperature T c of Mn1−x Pr x As (x = 0.005, 0.01, 0.015, 0.02) alloys. The absence of the huge magnetic entropy change $$\Delta {S}$$ spike which was calculated by the Maxwell relation is observed in the temperature range where the stepwise magnetic behaviors occur. The Clausius–Clapeyron equation is used to recalculate the $$\Delta {S}$$ of alloys Mn1−x Pr x As (x = 0.005, 0.01, 0.015, 0.02) under the conditions of the coexistence of the PM and FM phases. The maximum magnetic entropy change $$\Delta S_{M}^{\max }$$ of alloys Mn1−x Pr x As (x = 0.005, 0.01, 0.015, 0.02) for a 5 T field change decreases gradually from 30.2 J/kg K to 23.3 J/kg K as Pr increases from 0.005 to 0.02.

The Na0.5K0.5NbO3 single crystal was successfully grown by a seed-free solid-state crystal growth method using super-low content of LiBiO3 as a sintering aid. Microstructure, piezoelectric, ferroelectric and dielectric properties were investigated. The results show that well-paralleled lamellar ferroelectric ordering domains structure are present and no crack can be seen inside the single crystal. The best piezoelectric and dielectric properties (at 1 kHz) of d33 = 265 pC/N, Pr = 27.4 μC/cm2, e = 738, tanδ = 0.04 appear at x = 0.40at% for (1-x)Na0.5K0.5NbO3-xLiBiO3 single crystal. A higher remnant polarization Pr of 36.3 μC/cm2 were obtained at x = 0.45 at%.

The phase relations in the (1−x)Nd2Fe14B–xSm2Fe14B system over the whole concentration range have been studied by means of X-ray powder diffraction (XRD), differential thermal analysis (DTA) and scanning electron microscopy with energy-dispersive X-ray spectroscopy. Crystal structure parameters for all studied compositions of (Nd1−xSmx)2Fe14B have been determined by full-profile Rietveld refinements. These results revealed that all intermediate alloys of (Nd1−xSmx)2Fe14B are similar to the end member of the investigated system, Nd2Fe14B, with a tetragonal structure (space groupP42/mnm). The formation of continuous solid solutions has been found in this system. The normalized lattice parameters and unit-cell volumes of (Nd1−xSmx)2Fe14B solid solutions decrease linearly with increasing Sm content. The DTA measurements show that the melting temperature of (Nd1−xSmx)2Fe14B increases linearly with increasing Sm content and no metastable phases were detected. Based on the DTA data and XRD results, a tentative phase diagram for the pseudo-binary system Nd2Fe14B–Sm2Fe14B has been constructed.

The solid-state phase equilibria in the Fe–Ho–Pt ternary system at 1173 K (Ho ≤75%) were investigated by x-ray diffraction, scanning electron microscopy, and energy-dispersive x-ray spectroscopy techniques. The 1173 K isothermal section consists of 18 single-phase regions, 33 two-phase regions, and 16 three-phase regions. At 1173 K, we observed that the maximum solid solubility of Pt in Fe17Ho2, Fe23Ho6, Fe3Ho, and Fe2Ho is below 1 at.%. The binary phase Fe5Ho was not observed. The maximum solubility of Ho in α-Fe is about 1 at.%, and it is below 1.5 at.% in γ-(Fe, Pt), FePt, FePt3, and (Pt, Fe) (the solid solution of Fe in Pt). The existence of HoPt5, HoPt3, HoPt2, Ho3Pt4, HoPt, Ho5Pt4, Ho5Pt3, Ho2Pt, and Ho3Pt is confirmed, and the maximum solid solubility of Fe in them is below 1 at.%.

Large Na0.5K0.5NbO3 (NKN) piezoelectric single crystals were obtained by seed-free solid-state crystal growth method, which is a traditional sintering grain growth process, with LiBiO3 used as a sintering aid. The largest dimension of the single crystals obtained was 11 mm × 9 mm × 3 mm. In addition to the LiBiO3 doping content, temperature, and time effect of the crystal growth process was systematically investigated and considered from the kinetics point of view. With the assistance of Avrami analysis, parameters relevant to the crystal growth process were determined. Laue diffraction and transmission electron microscopy suggested an orthorhombic symmetry for the single crystalline structure. Dielectric-frequency-temperature measurements revealed an orthorhombic-tetragonal and tetragonal-cubic phase transition at 155°C and 405°C, respectively, both of which are typical of first-order transitions, and have a well-defined thermal hysteresis. Rayleigh analysis was performed regarding to the extrinsic reversible and nonreversible piezoelectric properties, and the result suggested a dominant intrinsic reversible piezoelectric contribution of 91.5% under E0 = 1 kV/cm AC amplitude. Such a single crystal growth process route is low cost and a relative simple preparation process.

(1−x)(Li0.05Na0.475K0.475)(Nb0.95Sb0.05O3)−xBiFeO3 ceramics were prepared by the conventional sintering method. The microstructure, phases and their relative volume fractions were investigated in detail by using transmission electron microscopy and X-ray diffraction. Fullprof and Topas softwares were also used to refine the X-ray diffraction data to confirm the crystal structure. The refinement results show that for x ≤ 0.008, the ceramics consists of the orthorhombic and tetragonal perovskite phases, and the fraction of the orthorhombic phase decreases from 50.66 % for x = 0.0 to 40.62 % for x = 0.008. When x = 0.01, the ceramics has a mixed microstructure with three coexisting phases: the orthorhombic, tetragonal perovskite phases and tetragonal tungsten bronze-type structure phase, and the fraction of the tetragonal tungsten bronze-type structure phase is 6.72 %. The selected area electron diffraction data is also consistent with the space groups for all of the above phases. This system also exhibits good ferroelectric and piezoelectric properties for applications, for example, at x = 0.004, the ceramic samples have a piezoelectric constant (d 33) of 272 pC/N and remanent polarization (P r) of 20.6 μC/cm2.

The isothermal section of the Dy-Mn-As ternary system at 773 K has been investigated by using x-ray diffraction, scanning electron microscopy and energy dispersive spectroscopy. This isothermal section consists of 12 single-phase regions, 21 two-phase regions and 10 three-phase regions. The highest solid solubility of Dy in MnAs is about 0.65 at.%Dy, and that of Mn in DyAs is less than 0.79 at.%Mn. The maximum solubility of As in DyMn2 is less than 0.33 at.%As. No ternary compound was found to exist in this section at 773 K.

The solid-state phase equilibria in the ternary Fe-Pt-Tb system in the compositional region below 75 at.%Tb at 1173 K have been studied by using x-ray diffraction, scanning electron microscopy and energy dispersion spectroscopy techniques. The 1173 K isothermal section consists of 18 single-phase regions, 33 two-phase regions, and 16 three-phase regions. At 1173 K, the maximum solid solubility of Pt in α-(Fe, Tb) is less than 2 at.%Pt and that of Pt in Fe2Tb, Fe3Tb, Fe23Tb6, Fe17Tb2 is below 1 at.%Pt; the compounds Pt5Tb, Pt3Tb, Pt2Tb, Pt4Tb3, PtTb, Pt4Tb5, Pt3Tb5, PtTb2, and PtTb3 are confirmed to exist at 1173 K and the highest solid solubility of Fe in them is below 1 at.% Fe; the maximum solid solubility of Tb in α-(Fe, Pt), γ-(Fe, Pt), FePt, FePt3, and (Pt, Fe) (namely, the solid solution of Fe in Pt) is about 1, 2, 1.9, 1.5, and 1.5 at.%Tb, respectively. No ternary compound was found to exist in this section at 1173 K.

The (1 − x)K0.5Na0.5NbO3–xAlFeO3 ((1 − x)KNN–xAF) (x = 0.01–0.08) lead-free piezoelectric ceramics were prepared at low temperature of 1,000 °C by conventional ceramic processing. And AF was used as a sintering aid in order to improve the sintering behavior of KNN. The effect of AF addition on the microstructure, dielectric and piezoelectric properties of the ceramics have been investigated. The results indicate that a small amount of AF can improve the sintering performance and piezoelectric properties of the ceramics effectively. The KNN–AF ceramics for x = 0.03 show the best piezoelectric properties: d 33 = 116 pC/N, k p = 32.9 %, Q m = 114.8, T C = 382 °C, P r = 21.8 μC/cm2. This also indicates that (1 − x)KNN–xAF ceramics are a promising lead-free piezoelectric candidate material because of its good properties, low-temperature sintering characteristics and plenty of Al2O3 and Fe2O3 resources with low cost.

The isothermal section of the Co–Pt–Dy system at 773 K was experimentally determined by combining results from X-ray diffraction, scanning electron microscopy and energy dispersive spectroscopy investigations. The presence of Co3Dy4 phase at 773 K is confirmed in this study. The four-phase region does not exist at 773 K in the ternary Co–Pt–Dy system, with instead two three-phase regions consisting of Co, DyPt, Dy3Pt4 and Co, DyPt2, Dy3Pt4, respectively. 23 single-phase regions (including solid solution regions of the binary compounds) and 21 three-phase regions were identified to exist at this isothermal section. The highest solid solubility of Dy in α1(Co, Pt), ∊(Co, Pt), α2(Co, Pt), CoPt, CoPt, α(Pt, Co) is less than 1.5 at.% Dy and that of Co in Dy3Pt, Dy2Pt, Dy5Pt3, Dy5Pt4, DyPt, Dy3Pt4, DyPt3, DyPt5 is below 1 at.% Co. The DyPt2 phase dissolves up to about 19 at.% Co. The maximum solid solubility of Pt in Co2Dy, Co3Dy, Co7Dy2, Co17Dy2 is approximately 1 at.% Pt. No new binary and ternary phases were found.

The effects of Pr on the microstructure and magnetic properties of PrxCo50-xPt50 alloys (x = 0, 0.2, 0.4, 0.6, 0.8, 1.0) were investigated. The XRD results indicate that all the alloys homogenized at 1000 °C contain only a single A1 (fcc) phase, while the alloys annealed at 675–750 °C consist of a hard-magnetic face-centered-tetragonal (fct) phase and a magnetically soft fcc phase. The (111) reflection belonging to the fct phase shifts to a higher angle and the c/a ratio increases as the Pr content increases, which leads to a decrease in the degree of ordering, S. Maximum values for the coercivity Hc and the remanence ratio mr are achieved in Pr0.4Co49.6Pt50 alloys annealed at 675 °C for 60 min. For the series of PrxCo50-xPt50 alloys annealed at 675 °C for 60 min, Hc decreases monotonically with increasing of Pr concentration, but mr is first enhanced and then weakened, showing a maximum value of 0.82 at x = 0.4 to 0.6.

The structure and magnetostriction of the high-Pr content (Tb 0.2 Pr 0.8 ) (Fe 0.4 Co 0.6 ) 1.88− x C 0.05 B x (0 ≤ x ≤ 0.08) alloys homogenized at 700 °C for 7 days have been investigated by X-ray diffraction and magnetic measurement. It was found that the matrix of the (Tb 0.2 Pr 0.8 ) (Fe 0.4 Co 0.6 ) 1.88− x C 0.05 B x alloys belongs to (Tb, Pr) (Fe, Co, C, B) 2 phase with MgCu 2 -type structure. The Curie temperatures are derived from M–T curves, which showed a slight increase when 0 ≤ x ≤ 0.06, then decreases with further increasing x . The composition dependence of magnetostriction λ a (= λ ∥ − λ ⊥ ) for (Tb 0.2 Pr 0.8 ) (Fe 0.4 Co 0.6 ) 1.88− x C 0.05 B x alloys reaches a maximum value at x = 0.01 at room temperature. The double split (4 4 0) lines of the Laves phase overlap gradually with increasing x and finally approach to form a broadened peak for x = 0.03. The spontaneous magnetostriction λ 111 decreases with increasing boron contents.

In this study, the Mg1−x Nd x Ni (x = 0, 0.05, 0.1, and 0.2) alloys were prepared by mechanical alloying (MA), and their electrochemical properties were measured by simulated battery test. It is observed that the introduction of Nd can accelerate the formation of the amorphous structure of MgNi alloy. With the increasing milling time from 40 to 60 h, the initial discharge capacity of Mg1−x Nd x Ni (x = 0, 0.05, 0.10, and 0.20) alloys increases gradually, while during the milling time from 60 to 70 h, it decreases. The maximum capacity of the Mg1−x Nd x Ni alloys is gradually reduced with increasing Nd content x. With the milling time t = 60 h and x = 0, the discharge capacity is increased up to 378.2 mAh/g. Experimental results show that partial substitution of Mg with Nd can improve cyclic stability of the amorphous MgNi sample at the expense of a reduction in the initial capacity.

The effects of Nd on the microstructure and magnetic properties of Nd x Co 50− x Pt 50 alloys ( x = 0, 0.5, 1.0, 1.5) were investigated. The XRD results indicated that all the alloys that were homogenized at 1000 °C mainly contain the A 1 (fcc) phase, while the alloys that were annealed at 675–750 °C consist of the hard magnetic face-centered-tetragonal (fct) phase and magnetically soft fcc phase. In any case, a few amount of NdPt 5 phase exists in alloys when x > 1.0. The (1 1 1) reflection belonging to fct phase shifts to a higher angle and the c/a ratio increases as the Nd content increases, which leads to the decrease in degree of ordering S . As a function of annealing time, both maximum values of the coercivity H c and remanence ratio m r were reached in Nd 0.5 Co 49.5 Pt 50 alloys annealed at 675 °C for 40 and 60 min, respectively. For the series of Nd x Co 50− x Pt 50 alloys annealed at 675 °C for 60 min, the H c decreases monotonically with the increase in Nd concentration but the value of m r is enhanced at first and then weakened, showing the highest value of 0.84 at x = 0.5.

The phase relationships in the Gd–Co–Al ternary system at 500°C have been investigated mainly by X-ray diffraction, scanning electron microscopy, and energy dispersion spectroscopy. The existence of two ternary compounds GdCo0.74Al1.26 and Gd2Co2Al has been confirmed. Twenty-two single-phase regions (including solid solution regions of the binary compounds), 43 two-phase regions, and 22 three-phase regions were found to exist at this isothermal section. In this work, no new binary or ternary phase was found.

The structure and magnetostriction of the (Tb 1− x Dy x ) 0.2 Pr 0.8 (Fe 0.4 Co 0.6 ) 1.88 C 0.05 intermetallic compounds (0≤ x ≤1) were studied by X-ray diffraction and magnetic measurements. The formation of an approximate single Laves phase with a MgCu2-type cubic structure was observed in this series of compounds. It was found that the Curie temperature and the saturation magnetization of the compounds would decrease with increase in the Dy content up to x =1. The magnetostriction λ a ( λ a = λ ‖ - λ ⊥ ) gently rises when x ≤0.6, and follows with a precipitous fall when x exceeds 0.6, with the highest value of λ a being reached in the compounds with x =0.6. The magnetostriction of all the samples was observed to approach their own saturation in the magnetic fields higher than 4 kOe. This indicates that the addition of a small amount of Dy could effectively improve the low-field magnetostriction of the Tb 0.2 Pr 0.8 (Fe 0.4 Co 0.6 ) 1.88 C 0.05 compounds, which could become a kind of promising magnetostrictive material.

The isothermal section of the Co–Pt–Nd system at 773 K was constructed in the whole concentration range by using X-ray diffraction, scanning electron microscopy, and energy dispersion spectroscopy techniques. Twenty-two single-phase regions (including solid solution regions of the binary compounds) were determined; 41 two-phase regions and 20 three-phase regions were identified to exist at this isothermal section. No new binary and ternary phases were found.

The isothermal section of the Pr–Pt–Co ternary system at 500 ∘ C has been determined in this study by X-ray diffraction, scanning electron microscopy and energy dispersion spectroscopy techniques. This isothermal cross-section consists of 20 single-phase regions (including solid solution regions of the binary compounds), 37 two-phase regions and 18 three-phase regions. The maximum solid solubility of Pt in Co 17 Pr 2 , Co 5 Pr, Co 19 Pr 5 ,Co 7 Pr 2 , Co 3 Pr,Co 2 Pr, Co 3 Pr 4 and CoPr 3 is less than 1 at.%Pt, and that of Co in PrPt, Pr 3 Pt 2 and Pr 7 Pt 3 below 1 at.%Co. The PrPt 5 phase dissolves up to 15 at.%Co and PrPt 2 up to 7.5 at.%Co. The highest solid solubility of Pr in α ( Co,Pt ) , e ( Co,Pt ) , α ( Co,Pt ) , CoPt 3 , CoPt and α ( Pt,Co ) is approximately 1.5 at.%Pr. No Co 2 Pr 5 phase and new ternary compounds were found.

Tb 0.3 Dy 0.7 Ho x Fe 1.95 ( x =0.00, 0.05, 0.10, 0.15, 0.20, 0.35, 0.50, 0.65) quaternary alloys were prepared by arc-melting and followed by annealing. The phases present and structure of the alloys were determined using a D8-Advance X-ray diffractometer. The magnetostriction of the alloys was studied by standard strain gauge technique. The dependence of Ho content on the structure, magnetostriction and density of the alloys was investigated in detail. The research results showed that Ho-doping did not change MgCu 2 -type cubic Laves structure in Tb 0.3 Dy 0.7 Fe 1.95 . When Ho content x ≤0.2, rich rare earth phase presented in the alloys increased and magnetostriction of the alloys reduced evidently with increasing x , but for alloys with x >0.2, the content of rich rare earth phase started to reduce and the magnetostriction increased quickly, especially at low magnetic field in the alloy with x =0.65 due to separation of rich rare earth phases on the surface of the alloy.

The effect of Nd addition on the structure, phase transformation and magnetic properties of FePt based alloys was investigated. The results indicated that the transition temperature from ordered FCT to disordered FCC phase decreased with increasing Nd concentration, but for alloys quenched rapidly from the γ phase region into ice-water, it increased with increasing Nd. The Nd element not only effectively reduced the grain size of the ordered phase but also decreased the degree of the ordered phase and refined the grains of the FCC matrix phase. The remanence ratio and coercivity of the FePt based alloy as a function of the Nd content had maximum values, respectively.

The effects of Pr on the structure and magnetic properties of PrxFe60.5-xPt39.5 alloys (x = 0, 0.5, 1.0. and 1.5) were investigated. X-ray diffraction data indicated that the phase transition temperature of FePt based alloys from disordered face-centered-cubic to ordered face-centered-tetragonal cubic decreases with the increase in Pr concentration. Pr plays the role of a grain refiner and it can enhance the exchange coupling between soft magnetic phase and hard magnetic phase. The results indicate that the replacement of Fe by Pr can significantly improve the remanence and coercivity of the Fe60.5Pt39.5 alloy. These results can be explained on the basis of phase transformation and microstructure. Both the remanence ratio and coercivity of the FePt based alloy as a function of the Pr content are increased by the optimum addition of 0.5 at.% Pr.

The solid state phase equilibria in the Fe–Pt–Dy ternary system at 900 °C (Dy ≤ 75 at.%) were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersion spectroscopy (EDS) techniques. It is found that the 900 °C isothermal section consists of 18 single-phase regions, 33 two-phase regions and 16 three-phase regions. At 900 °C, it is observed that the maximum solid solubility of Pt in Fe 2 Dy and α-(Fe, Dy) is 5 at.% Pt and 3 at.% Pt, respectively. The binary phase Fe 5 Dy was not observed. The existence of DyPt 5 , DyPt 3 , DyPt 2 , Dy 3 Pt 4 , DyPt, Dy 5 Pt 4 , Dy 5 Pt 3 , Dy 2 Pt and Dy 3 Pt compounds is confirmed and the maximum solubility of Fe in them is below 1 at.% Fe; the maximum solubility of Dy in α-(Fe, Pt), γ-(Fe, Pt), FePt, FePt 3 and (Pt, Fe) (the solid solution of Fe in Pt) is 3 at.% Dy, 2 at.% Dy, 2 at.% Dy, 1.5 at.% Dy and 1.5 at.% Dy, respectively.