Structural Analysis of Sr3NbFe3Si2O14 Single Crystal from the Langasite Family and Finding of Negative Thermal Expansion in the Range of 83–110 K

Abstract

Iron-containing Sr3NbFe3Si2O14 single crystals from the langasite family, which are interesting for researchers due to their magnetic ordering at T N = 26 K, have been grown by the floating zone melting method. Accurate X-ray diffraction analysis is performed at 293 and 90.5 K using the data collected on a CCD diffractometer. To compensate for systematic errors, two data sets are collected at each temperature. The structure is refined based on averaged data set: sp. gr. P321, Z = 1, sin θ/λ ≤ 1.35 A–1; a = 8.2609(4) A, c = 5.1313(3) A at 293 K and a = 8.2344(6) A, c = 5.1243(6) A at 90.5 K; the agreement factors are R/wR = 1.18/1.03% and Δρmin/Δρmax =–0.57/0.25 e/A3 for 3583 independent reflections at 293 K and R/wR = 1.18/1.13% and Δρmin/Δρmax =–0.54/0.23 e/A3 for 3638 reflections at 90.5 K. Negative thermal expansion in the direction of the cell c axis is revealed in the range of 83–110 K.