Synthesis, structure and dielectric properties of new ordering perovskites LnPbMgSbO6 (Ln = La, Pr, Nd)

• Ordered double perovskites LnPbMgSbO6 (Ln = La, Pr, Nd) were synthesized.
• The crystal structures with different rare earth ions at A-site have been studied.
• Chemical pressure is induced by substituting different Ln3+ ions.
• Raman spectra are assigned to definite vibrations of the structure.
• Dielectric properties under different frequencies have been investigated.

The synthesis, crystal structure, and dielectric properties of the titled compounds were described. The structural symmetry was determined to be monoclinic P21/n (No. 14) space group. Based on the highly ordered array of alternating MgO6 and SbO6 octahedra, these double perovskites exhibited significant octahedral tilting distortion according to the Glazer's notation system a−a−c+. As the result of substituting different rare earth ions from La3+ to Nd3+, both the tolerance factor (t) and coordination number (CN) were reduced simultaneously and the B-site lattice distorted more heavily with the increase in chemical pressure by adopting smaller Ln3+ ion. For the investigation of dielectric properties, all the samples consistently presented weak frequency dependent characteristic with relatively low dielectric constant (ε') and low tangent loss (tanδ). With the shrinkage of the Ln3+ ion size, the corresponding ε' decreased remarkably and the dispersive tanδ peaks around 300 K shifted to low temperature, indicating that the space-charge-hopping mechanism dominated permittivity property can be tuned by controlling the degree of lattice distortion via substituting different Ln3+ ions.

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