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Abstract Magneto‐caloric materials offer the possibility to design environmentally friendlier thermal management devices compared to the widely used gas‐based systems. The challenges to develop this solid‐state based technology lie in the difficulty of finding materials presenting a large magneto‐caloric effect over a broad temperature span together with suitable secondary application parameters such as low heat capacity and high thermal conductivity. A series of compounds derived from the PbFCl structure is investigated using a combination of computational and experimental methods focusing on the change of cell volume in magnetic and non‐magnetic ground states. Scaling analysis of the magnetic properties determines thatmore » they are second order phase transition ferromagnets and that the magnetic entropy change is driven by the coupling of magneto‐elastic strain in the square‐net through the magnetic transition determined from neutron and synchrotron X‐ray diffraction. The primary and secondary application related properties are measured experimentally, and the c/a parameter is identified as an accurate proxy to control the magnetic transition. Chemical substitution on the square‐net affords tuning of the Curie temperature over a broad temperature span between 252 and 322 K. A predictive machine learning model for the c/a parameter is developed to guide future exploratory synthesis.« less

Inorganic phosphor materials play a crucial role in the creation of white light from blue and near-UV solid-state light-emitting diodes. Understanding the intricacies of the phosphor structure is key for setting the stage for improved, more efficient functionality. Average structure and coordination environment analysis of the robust and efficient green-emitting phosphor, β-SiAlON:Eu²⁺ (β-Si_6–zAl_zO_zN_8–zEu_0.009), is combined here with a range of property measurements to elucidate the role of Al content (z) in luminescence properties, including the red shift of emission and the thermal quenching of luminescence as a function of increasing Al content z. Average structure techniques reveal changes in polyhedralmore » distortion with increasing z for the 9-coordinate Eu site in β-SiAlON:Eu²⁺. X-ray absorption near edge structure (XANES) is used to confirm that the majority of the activator Eu is in the Eu²⁺ state, exhibiting the symmetry-allowed and efficient 4f⁷5d⁰ → 4f⁶5d¹ transitions. As a result, room temperature and temperature-dependent luminescence indicate a curious increase in thermal stability with increasing z over a small range due to an increasing barrier for thermal ionization, which is correlated to an increase in the quantum yield of the phosphor.« less

Following the recent discovery of a new family of hybrid ABX₃ perovskites where X=(H₂POO)^- (hypophosphite), this paper reports a facile synthesis for mixed X-site formate perovskites of composition [GUA]Mn(HCOO)_3-x(H₂POO)_x, with two crystallographically distinct, partially ordered intermediate phases with x=0.84 and 1.53, corresponding to ca. 30 and 50 mol % hypophosphite, respectively. These phases are characterised by single-crystal XRD and solid-state NMR spectroscopy, and their magnetic properties are reported.

Eu2+ inserted in beta-Si3-xAlxOxN4-x is a material that shows exceptional promise as a green-emitting phosphor. Synchrotron X-ray and neutron scattering, in conjunction with first-principles calculations and Eu L-3 X-ray absorption measurements, yield a consistent picture of the composition, and the favorable position for Eu2+ substitution in the crystal structure. The Debye temperature Theta(D), which is a proxy for structural rigidity relating to effectiveness as a phosphor, is very high for the starting beta-Si3N4 framework and is determined to decrease only slightly for the small amounts of Al3+ and O2- co-substitution that are required for charge balance associated with Eu2+ insertion.more » (C) 2014 AIP Publishing LLC.« less