Aurivillius Phase Bi₄V₃O₁₂ with d¹ Magnetic Cations, Anisotropic and Negative Thermal Expansion, Multiple Structural...

Aurivillius phases are an important class of inorganic compounds as they often show ferroelectric properties, and some members of this family are used in nonvolatile ferroelectric memories. The majority of Aurivillius phases have nonmagnetic d⁰ cations in the perovskite block. Bi₄Ti₃O₁₂ is the best-known and extensively studied compound within this family. Here, using a high-pressure, high-temperature synthesis method, we could successfully prepare a full magnetic analogue, Bi₄V₃O₁₂, with d¹ cations. Bi₄V₃O₁₂ is unstable in air above about 520 K. However, in an inert atmosphere, Bi₄V₃O₁₂ demonstrates two first-order reversible structural transitions near 525 and 760 K. The high-temperature prototypical phase is the same in both Bi₄V₃O₁₂ and Bi₄Ti₃O₁₂ with tetragonal (T) I4/mmm symmetry and a_T = 3.85608(5) Å and c_T = 32.6920(8) Å (at 850 K) for Bi₄V₃O₁₂, while the low-temperature phases are different. Bi₄V₃O₁₂ shows anisotropic thermal expansion above 300 K and negative volumetric thermal expansion above about 700 K. Magnetic measurements showed a broad maximum near 70 K on magnetic susceptibility, indicating the presence of low-dimensional magnetism with strong antiferromagnetic interactions between V⁴⁺ ions with the Curie-Weiss temperature of about -370 K. But no long-range magnetic ordering was found in Bi₄V₃O₁₂ down to 2 K.