Growth and X-ray Diffraction Study and Specific Features of Thermal Expansion of Ba₃NbFe₃Si₂O₁₄ Single Crystal from the Langasite Family

Abstract

Ba3NbFe3Si2O14 single crystals of promising multiferroic properties from the langasite family have been grown by floating zone melting. The accurate high-resolution X-ray diffraction studies of this crystal were performed on a diffractometer with a two-dimensional CCD detector at 293 and 90.5 K. To compensate systematic measurement errors, two data sets were obtained independently for different sample orientations at each temperature. The structure refinement was performed based on averaged data sets with the following results: space group P321, Z = 1; a = 8.52421(8), c = 5.23372(5) Å at 293 K; and a = 8.5211(2), c = 5.2243(7) Å, at 90.5 K. The R factors of the model structure refinement were found to be R/wR = 1.15/1.29% for 4396 independent reflections at 293 K, and R/wR = 1.13/1.35% for 4203 reflections at 90.5 K. A displacement of magnetic ion Fe3+ in the 3f site was found with reducing temperature. It was also established from comparison of the structures of Ba3NbFe3Si2O14 and Ba3TaFe3Si2O14 that the mobility of the cation in the 3f sites changes with an isomorphic substitution of Nb cations by Ta in the octahedral sites. This can change the characteristics of the structure and magnetic helix responsible for multiferroic properties of the iron-containing langasites. An anomaly in thermal expansion is found in the Ba3NbFe3Si2O14 crystal. When the temperature is reduced, the compression ratio along the c axis is about two times larger than that along the a axis, which is not typical of other langasite-family crystals.

Absolute crystal and magnetic chiralities in the langasite compound Ba3NbFe3Si2O14 determined by polarized neutron and x-ray scattering

“…To finally corroborate the validity and robustness of our results we have used the structure model proposed in Ref. [19] to calculate the Schwinger flipping ratios. As a matter of fact the calculated values only differ in the fourth decimal digit, while our measured flipping ratios have an uncertainty of at least 0.001.…”

Pressure Induced Spin Crossover and Magnetic Properties of Multiferroic Ba3NbFe3Si2O14

“…In particular, when iron ions partially occupy the 2 d tetrahedral sites, replacing Si, a very strong magnetic interaction can appear between the Fe(3 f ) and Fe(2 d ) ions in the ( ab ) plane, since the Fe(3 f )-O2(6 g )-Fe(2 d ) bond distances and the bond angle are very effective for strong superexchange interaction [ 10 , 20 ]. In addition, under high pressure, Fe ions can partially be redistributed between tetrahedral 3 f and octahedral 1 a sites in the nearest layers along the c axis ( Figure 1 ).…”

“…At ambient conditions, BNFS has a trigonal crystal structure (space group P 321, point group 32, Z = 1), where layers of oxygen tetrahedrons with Fe(3 f ) and Si(2 d ) ions alternate with the layers containing Nb(1 a ) and Ba(3 e ) ions, which are located in oxygen octahedrons and Thompson cubes, respectively [ 1 , 10 ] ( Figure 1 ).…”