Crystal structures and magnetocaloric properties of Li₅ASrMB₁₂O₂₄ (A = Mg, Zn; M = Cr, Ni)

Three new transition-metal-based borate crystals, Li₅MgSrMB₁₂O₂₄ (M ​= ​Cr, Ni) and Li₅ZnSrNiB₁₂O₂₄, were obtained using the high temperature solution method. Their structures were determined by the single crystal X-ray diffraction, which crystallize in the trigonal R 3¯ space group. The [B₃O₁₁] groups in the structures lead to the long distance between two nearest magnetic ions, which can reduce the interaction of adjacent magnetic centers. The magnetic properties and thermal stabilities of the title compounds were also investigated. The results indicated that Li₅MgSrCrB₁₂O₂₄ has stable chemical-physical properties and its maximum –ΔS_m value of 14.33 ​J ​kg⁻¹·K⁻¹ at 2 ​K for Δμ₀H ​= ​9 ​T reaching 88.6% of the theoretical paramagnetic limit, suggesting its potential application on the magnetic refrigeration.