Search

Here we report on a detailed investigation of the crystal structure, cryogenic magnetic and magneto-caloric properties in Ho 2 BaCuO 5 cuprate. The Ho 2 BaCuO 5 crystallized in the orthorhombic crystal structure with Pbnm space group and undergoes a paramagnetic (PM) to antiferromagnetic (AFM) transition at the Néel temperature ( T N ) of 12.5 K. An obvious signal change in the magneto-caloric effect (MCE) was observed, which is correlated with the fact of the AFM ground state inducing a small negative magnetic entropy change (-Δ S M ) at/below T N and a field-induced metamagnetic transition (first ordered) from AFM to ferromagnetic (FM) producing a large positive -Δ S M above T N . For a magnetic field change of 0–7 T, the -Δ S M max ≈ 10.4 J/kg K, RCP ≈ 263 J/kg and RC ≈ 199 J/kg for the maximum magnetic entropy change, relative cooling power and refrigerant capacity are evaluated, respectively. [ABSTRACT FROM AUTHOR]

In this work, polycrystalline oxides viz., Ho 2 CrMnO 6 (HCMO) and Er 2 CrMnO 6 (ECMO), were prepared using the sol-gel process, and their crystal structure, magnetic properties, and magnetocaloric effects (MCEs) were studied. X-ray refinement results demonstrate that both oxides exhibited the B -site disordered perovskite type structure (Pbnm space group). A ferromagnetic-paramagnetic phase transition as well as large reversible MCEs was also observed at Curie temperatures (T C) of ~6.1 and ~5.2 K for HCMO and ECMO, respectively. For a magnetic field change (ΔH) of 0–7 T, the maximum magnetic entropy change (-Δ S M), temperature-averaged entropy change (TEC 3), and relative cooling power (RCP) were estimated to be 11.03 J/kgK, 11.02 J/kgK, and 322.7 J/kg for HCMO, and 12.94 J/kgK, 12.80 J/kgK and 277.5 J/kg for ECMO. [ABSTRACT FROM AUTHOR]

In this paper, weakly agglomerated and well dispersed α-Al 2 O 3 powders were synthesized by a novel spray precipitation method. It was demonstrated that the as-prepared powders exhibited better dispersity than powders from conventional precipitation due to the increased phase contact and reaction area during the precipitation process. The effects of different titration ways, calcination temperature and holding time on the morphology, phase composition and sintering behaviour of Al 2 O 3 powders were systematically investigated. Weakly agglomerated and well crystallized α-Al 2 O 3 powders were obtained when the as-prepared precursors were calcined at 1150 °C for 2 h in air. The average particle size of α-Al 2 O 3 powders with higher sintering activity was approximately 68.6 nm, and the specific surface area was above 22.4 m 2 g −1 . [ABSTRACT FROM AUTHOR]

Y 2 O 3 transparent ceramics were fabricated from precipitated powders prepared at different stirring speeds during the precipitation process. The influence of the stirring speed on the phase component of precursors, morphology of Y 2 O 3 powders and properties of fabricated ceramics were systematically investigated. Crystalline phase precursors of (NH 4 ) a Y(OH) b (CO 3 ) c ·H 2 O were prepared from 110 rpm, 220 rpm and 550 rpm respectively. But amorphous precursors of Y(CO 3 )(OH)·nH 2 O (n = 1–1.5) were observed when stirring speeds were 330 rpm and 440 rpm. Y 2 O 3 powders prepared from 440 rpm exhibited the lowest agglomeration and the smallest grain size, and the ceramics with the optimal transmittance was accordingly obtained. The results of computational fluid dynamics software CFX showed that a more homogeneous flow field distribution without local circulations could be produced at 440 rpm, which would be benefit for the optical quality of transparent ceramics. The study would provide a considerable reference for the controllable fabrication of well-dispersibility Y 2 O 3 powders and Y 2 O 3 transparent ceramics. [ABSTRACT FROM AUTHOR]