Synthesis, structural analysis and dielectric properties of the double-layer Aurivillius compound Pb1-2Bi1.5+2La0.5Nb2-Mn O9

Abstract

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.

Synthesis of Aurivillius Phase CaBi4Ti4O15 Doped with both La3+ and Mn3+ Cations: Crystal Structure and Dielectric Properties

“…Furthermore, the Ti 4+ could be simultaneously substituted by Mn 3+ up to 15% molar ratio Ti 4+ with adjusted the Ca:Bi ratio as the nominal formula for x = 0.6. The substitution of Mn 3+ on the B-site cation up to 15% molar ratio has been reported in our previous reports both for four-layer Aurivillius Pb 1-x Bi 4+x Ti 4-x Mn x O 15 and double-layer Aurivillius Pb 1-2x Bi 1.5+2x La 0.5 Nb 2-x Mn x O 9 synthesized by the molten salt method 8,9 . The presence of impurities for x = 0.8 and 1 is suggested due to the oxidizing Mn 3+ to Mn 4+ in samples.…”

“…The dielectric constant value at 100 kHz increases as x increases, where the value is 206.03, 342.4, 491.11, and 868.41 for x = 0, 0.2, 0.4, and 0.6, respectively. It was reported that the presence of A-site cations with 6s 2 lone pair electrons such as Bi 3+ strongly favors a highly distorted structure, resulting in increased polarization 8,20 . According to the nominal formula, the substitution of Mn 3+ for Ti 4+ on the B-site was compensated by the increasing proportion of Bi 3+ cations, which could result in the higher distortion of BO 6 octahedra.…”

“…Furthermore, the tan δ values of single-phase samples increase with increasing x with value 0.0166 for x = 0 to 0.0834 for x = 0.2, 0.2473 for x = 0.4, and 0.5291 for x = 0.6 at 100 kHz. The substitution of Mn 3+ for Ti 4+ increase in the unpaired electron concentrations as the charge carriers, which results in the higher electrical conductivity 8 . Besides, the formation of the mixed-valent Mn 3+ and Mn 4+ in the higher x, as discussed in the refinement results above, probably induced the electron transport via Mn 3+ -O-Mn 4+ double-exchange interaction contributing to a significant increase in dielectric loss value of x = 0.4 and 0.6 samples.…”

“…Several magnetoelectric materials based on Aurivillius phase have been reported for formula Pb 1-2x Bi 1.5+2x La 0. 18 , and exhibited the improvement in dielectric properties [8][9][10] .…”

Investigation on structure, dielectric and magnetic properties of the four-layer Aurivillius phase Pb1-Bi3.5+Nd0.5Ti4-Mn O15 prepared via molten salt method

“…Referring to the ionic radius of Pb 2þ (1.49 Å) and Bi 3þ (1.31 Å) for 12-fold coordination and the ionic radii of Mn 3þ (0.645 Å) and Ti 4þ (0.605 Å) for 6-fold coordination [18,19], the decreased cell volume is strongly affected by the increasing proportion of smaller Bi 3þ and the decreasing proportion of larger Pb 2þ , according to the nominal formula of Pb 1-x Bi 3.5þx Nd 0.5 Ti 4-x Mn x O 15 . These compositional changes resulted in the higher distortion of the BO 6 octahedra, by which the structure becomes more orthorhombic [20,21]. This distortion led to the tilting of BO 6 octahedra along the a-axis, confirmed by the increased difference between the a and b lattice parameter [22].…”