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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.

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 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.%.

(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.

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 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.