research papers 676 doi:10.1107/S2052520614006611 Acta Cryst. (2014). B70, 676–680 Acta Crystallographica Section B Structural Science, Crystal Engineering and Materials ISSN 2052-5206 Crystal structure and thermal expansion of Mn 1x Fe x Ge Vadim Dyadkin, a,b * Sergey Grigoriev, b,c Sergey V. Ovsyannikov, d Elena Bykova, d Leonid Dubrovinsky, d Anatoly Tsvyashchenko, e L.N. Fomicheva e and Dmitry Chernyshov a a Swiss–Norwegian Beamlines at the European Synchrotron Radiation Facility, 38000 Grenoble, France, b Petersburg Nuclear Physics Institute, 188300 Gatchina, Saint-Petersburg, Russia, c Saint-Petersburg State University, Ulya- novskaya 1, 198504 Saint-Petersburg, Russia, d Bayerisches Geoinstitut, University of Bayreuth, D-95440 Bayreuth, Germany, and e Institute for High Pressure Physics, Russian Academy of Sciences, 142190 Troitsk, Moscow, Russia Correspondence e-mail: diadkin@esrf.fr # 2014 International Union of Crystallography A series of temperature-dependent single-crystal and powder diffraction experiments has been carried out using synchro- tron radiation in order to characterize the monogermanides of Mn, Fe and their solid solutions. The MnGe single crystal is found to be enantiopure and we report the absolute structure determination. The thermal expansion, parametrized with the Debye model, is discussed from the temperature-dependent powder diffraction measurements for Mn 1x Fe x Ge (x = 0, 0.1, 0.2, 0.25, 0.3, 0.4, 0.5, 0.6, 0.7, 0.75, 0.8, 0.9). Whereas the unit- cell dimension and the Debye temperature follow a linear trend as a function of composition, the thermal expansion coefficient deviates from linear dependence with increasing Mn content. No structural phase transformations have been observed for any composition in the temperature range 80– 500 K for both single-crystal and powder diffraction, indi- cating that the phase transition previously observed with neutron powder diffraction most probably has a magnetic origin. Received 6 December 2013 Accepted 25 March 2014 1. Introduction An interest in monosilicides and monogermanides of manga- nese, iron and cobalt is motivated by their unusual magnetic and transport properties (Stishov & Petrova, 2011) exempli- fied by chiral magnetic orderings including so-called skyrmion structures (Kanazawa et al., 2012; Grigoriev et al. , 2013) and topological contributions to magneto-resistance and Hall effect (Kanazawa et al., 2011). Due to these properties, monosilicides and monogermanides are considered as poten- tial candidates for the next generation of high-speed and low- energy magnetic storage devices (Duine, 2013). Among these compounds, the monogermanides of Mn and Co are less well characterized than monosilicides due to their difficult synth- esis that requires high temperature and pressure (Takizawa et al., 1988). Until now, the magnetism and crystal structure have been studied only for MnGe and CoGe powders (Takizawa et al., 1988; Kanazawa et al., 2011, 2012; Makarova et al., 2012); the magnetic properties of FeGe and its crystal structure are characterized from single-crystal data (Lebech et al., 1989; Wilhelm et al., 2007). Recently, a new series of chiral helimagnets was synthesized in the form of powder (Mn 1x Fe x Ge with x = 0, 0.1, 0.2, 0.25, 0.3, 0.4, 0.5, 0.6, 0.7, 0.75, 0.8, 0.9) using the method described by Tsvyashchenko (1984). The magnetic properties of these compounds have been characterized by microscopic measurements and small-angle neutron diffraction (Grigoriev et al., 2013). The temperature of the magnetic ordering and the magnetic wavevector show non-monotonic behavior as a