The double-layer Aurivillius phases Pb 1-2x Bi 1.5+2x La 0.5 Nb 2-x Mn x O 9 (x = 0, 0.1, 0.3, and 0.5) were synthesized by a molten salt method using a mixture of K 2 SO 4 /Na 2 SO 4 . The effect of composition on the structure, morphology and dielectric properties was investigated. X-ray diffraction showed that single-phase samples with a non-polar, orthorhombic A2 1 am structure were obtained for x = 0, 0.1 and 0.3. The unit cell becomes more orthorhombic with increasing x as the degree of distortion of the BO 6 octahedra in the perovskite layer increases. Raman spectroscopy showed the typical modes of the orthorhombic double-layer Aurivillius structure and indicated that the La 3+ ions prefer to occupy the perovskite A-site, Mn 3+ occupies the B-site, and the Pb 2+ ions are found in the Bi 2 O 2 layer. The morphology of the samples was probed by scanning electron microscopy, which showed anisotropic, plate-like crystallites that increased in size with increasing x. The dielectric constant significantly increased with x, and the ferroelectric properties became more relaxor-like.

Textural evolution and improved ductility in Zn-0.2Mg-0.8Mn (wt%) alloys at different extrusion temperatures

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The double-layer Aurivillius phase Pb 0.4 Bi 2.1 La 0.5 Nb 1.7 Mn 0.3 O 9 was synthesized by a molten salt method using a K 2 SO 4 /Na 2 SO 4 flux. The effect on the crystal structure, morphology, dielectric and magnetic properties of varying the molar ratio of the oxide precursors to salt flux was investigated. Single-phase products with an orthorhombic structure were obtained for oxide to salt ratios of between 1:5 and 1:9, whereas for lower concentrations of salt a pyrochlore impurity phase is found in the products. SEM showed anisotropic plate-like grains, the size of which increases for larger salt ratios. An investigation of the magnetic properties showed the presence of mixed Mn 3+ and Mn 4+ ; the unit cell volume of the single-phase products decreases as the proportion of salt increases, which implies a higher proportion of smaller Mn 4+ cations. This can be explained by the oxide ion donating properties (oxobasicity) of the molten salt mixture, which produces an oxidizing environment during synthesis. The best dielectric properties are obtained for an oxide to salt ratio of 1:7, exhibiting relaxor ferroelectric behavior. This is also the ratio at which the most pronounced ferromagnetic properties are observed, resulting from double-exchange interactions between Mn 3+ and Mn 4+ , the proportions of which are approximately equal. Pb 0.4 Bi 2.1 La 0.5 Nb 1.7 Mn 0.3 O 9 synthesized under these conditions thus exhibits optimal multiferroic properties.