Diffusion couples based upon Cu2Se/In2Se3 pairings have been examined in order to identify the kinetics of intermediate phase development and the associated phase equilibria. For the diffusion couples annealed at 550 °C for 1.5 h, all phases included in the Cu2Se–In2Se3 pseudobinary phase diagram section developed including the CuInSe2 (CIS) phase. Also, the In6Se7 phase formed for annealing times in excess of 1.5 h at 550 °C, indicating a modification of the diffusion pathway outside the pseudobinary phase diagram section. The growth of the CIS phase formed by reactive diffusion follows parabolic kinetics (x2=kt) with the k value of 3.3×10−8 cm2/s. CIS phase precipitates with a dendritic morphology are also produced within the Cu2Se side of the diffusion couple far from the initial interface, indicating that In is the fast component during interdiffusion. Based upon electron diffraction analysis and simulation of electron diffraction patterns, the dendritic shaped CIS precipitate structure was uniquely determined to be the metastable zinc blende type rather than the stable chalcopyrite-type structure. The structure and orientation relationship between the metastable CIS phase and the Cu2Se matrix satisfy the conditions established for the development of a solid state dendritic morphology.

The crystal structure, cryogenic magnetic properties, and magnetocaloric performance of double perovskite Eu₂NiMnO₆ (ENMO), Gd₂NiMnO₆ (GNMO), and Tb₂NiMnO₆ (TNMO) ceramic powder samples synthesized by solid-state method have been investigated. X-ray diffraction structural investigation reveal that all compounds crystallize in the monoclinic structure with a P2₁/n space group. A ferromagnetic to paramagnetic (FM-PM) second-order phase transition occurred in ENMO, GNMO, and TNMO at 143, 130, and 112 K, respectively. Maximum magnetic entropy changes and relative cooling power with a 5 T applied magnetic field are determined to be 3.2, 3.8, 3.5 J/kgK and 150, 182, 176 J/kg for the investigated samples, respectively. The change in structural, magnetic, and magnetocaloric effect attributed to the superexchange mechanism of Ni²⁺–O–Mn³⁺ and Ni²⁺–O–Mn⁴⁺. The various atomic sizes of Eu, Gd, and Tb affect the ratio of Mn⁴⁺/Mn³⁺, which is responsible for the considerable change in properties of double perovskite.

The ΔT_ad values are high and reach their maximum within a narrow temperature range below 20 K. This indicates that Dy_1−xEr_xNi₂ solid solutions may be a viable option for refrigerants in magnetic cryocoolers suitable for hydrogen liquefaction.