Evidence of a Large Refrigerant Capacity in Nb-Modified La1.4Sr1.6Mn2−xNbxO7 (0.0 ≤ x ≤ 0.15) Layered Perovskites
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Date
2024-03
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Abstract
In this work, evidence of isothermal magnetic entropy change (∆SM) over a broad tempera ture region is presented in a series of La1.4Sr1.6Mn2−xNbxO7 Ruddlesden–Popper compounds with
niobium modification (Nb) (0.0 ≤ x ≤ 0.15) at the manganese (Mn) site. The ceramic samples were ob tained through a solid-state sintering method in optimized conditions. All compounds predominantly
possessed Ruddlesden–Popper phase while a few additional reflections were resolved in Nb-doped
compounds which indicates the separation of structural phases. These peaks are assigned to a sepa rate layered perovskite and single perovskite with tetragonal symmetry and hexagonal symmetry,
respectively. The microstructure of the pure sample reveals uniform grain morphology but in Nb doped specimens chiefly three types of grains were found. It was assumed that the inter-connected
large particles were of R-P phase which is dominant in both parent and x = 0.05 compounds, while
the hexagonal and polygonal morphology of grains in higher concentrations of dopants directly
corroborates with the symmetry of single perovskite and additional layered perovskite phases, re spectively. The parent compound exhibits a single ∆SM curve, whereas all Nb-substituted samples
display bifurcated ∆SM curves. This indicated two transition regions with multiple magnetic com ponents, attributed to distinct structural phases. The highest ∆SM values obtained for components
corresponding to the R-P phase are 2.32 Jkg−1k
−1
, 0.75 Jkg−1k
−1
, 0.58 Jkg−1k
−1 and 0.43 Jkg−1k
−1
and for the second component located around room temperature are 0.0 Jkg−1k
−1
, 0.2 Jkg−1k
−1
,
0.28 Jkg−1k
−1 and 0.35 Jkg−1k
−1
for x = 0.0, 0.05, 0.10 and 0.15 compositions, respectively, at 2.5 T.
Due to the collective participation of both components the ∆SM was expanded through a broad
temperature range upon Nb doping.