Solid State Sciences 7 (2005) 1492–1499 www.elsevier.com/locate/ssscie Structural and magnetic properties of the solid solution (0  x  1) YMn 1−x (Cu 3/4 Mo 1/4 ) x O 3 Sylvie Malo a,∗ , Antoine Maignan a , Sylvain Marinel a , Maryvonne Hervieu a , Kenneth R. Poeppelmeier b , Bernard Raveau a a Laboratoire CRISMAT, UMR CNRS ENSICAEN 6508, 6 bd Maréchal Juin, 14050 Caen Cedex 4, France b Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, IL 60208-3113, USA Received 14 June 2005; accepted 27 July 2005 Available online 25 October 2005 Abstract Recently, the ferroelectromagnet YMnO 3 has been the focus of interest because it exhibits both antiferromagnetism (Néel temperature ∼ 80 K) and ferroelectricity (Curie temperature ∼ 914 K). There have been no reports of complete YMn 1−x M x O 3 solid solutions in which substitution of the foreign M cation preserves the hexagonal P6 3 cm structure. In contrast there exist several homeotypic phases with the general formula, Ln 1+n Cu n MO 3+3n (n = 1(M = Ti), 2 (M = V) and 3 (M = Mo); Ln: lanthanide). Several YMn 1−x (Cu 3/4 Mo 1/4 ) x O 3 compounds have been synthesized. The solid solution, from YMnO 3 (x = 0) to YCu 3/4 Mo 1/4 O 3 (x = 1) has been characterized by X-ray diffraction and transmis- sion electron microscopy study. For 0 <x< 0.9, the compounds are found to crystallize in the non-centrosymmetric structure, space group P6 3 cm, of YMnO 3 . The Mn-free end member, x = 1, crystallizes in a complex multiple cell, the superstructure being associated to Cu 3+ /Mo 6+ cationic ordering. Dilution of the Mn 3+ magnetic array by the paramagnetic (Cu 2+ ) and diamagnetic (Mo 6+ ) cations is found to decrease the antiferromagnetic ordering temperature and it becomes undetectable for x  0.5 compositions.  2005 Elsevier SAS. All rights reserved. Keywords: Hexagonal structure; Electron Microscopy; Solid solution; Magnetic properties 1. Introduction Among the fascinating properties of the perovskite mangan- ites, the ferroelectricity of the hexagonal phase “type YAlO 3 ” has been revisited after the new interest of the solid state scien- tists for the search of new multiferroïc materials (see Ref. [1] and references therein), which are promising materials for ap- plications in the information storage spintronics and sensor. Those properties result from the strong interplay between spin, charge and orbital ordering, responsible for simultaneous fer- romagnetism, ferroelectricity and ferroelasticity. The YMnO 3 hexagonal phase is a typical example of a magnetic ferroelectric with a magnetic Néel temperature T N ∼ 80 K and a ferroelec- tric Curie temperature T C ∼ 914 K [2–5]. For this phase a clear anomaly in the dielectric constant at T N has been found [5]. * Corresponding author. Tel.: +33 2 31 45 26 10. E-mail address: sylvie.malo@ensicaen.fr (S. Malo). From the structural point of view, the RMnO 3 hexagonal structure differs strongly from the ideal cubic and distorted orthorhombic perovskite and is generally stabilized for small enough R cation in RMnO 3 (R are lanthanides smaller than Tb 3+ , Sc 3+ and Y 3+ ) [2,6,7]. The Mn cations adopt a fivefold trigonal bipyramidal coordination contrasting with its octahe- dral coordination in the “classical” perovskite. Accordingly, the framework of the hexagonal phase (space group P6 3 cm) is built from the stacking along the c-axis of layers built of corner sharing (MnO 3 ) trigonal bipyramids (Fig. 1). This coordina- tion of Mn leads to a crystal field splitting, different from the octahedral one, with an unoccupied d 2 z orbital hybridized with the p z orbital of oxygen along the c-direction. This has been previously proposed to be at the origin of a “one-dimensional d 0 -ness” which is original compared to usual “d 0 -ness criteri- on” for ferroelectricity [8]. There exist only a few reports describing substitutions at the Mn-site in YMnO 3 , which preserve the hexagonal structure. As for the substitution of cobalt for manganese in YMnO 3 , though 1293-2558/$ – see front matter  2005 Elsevier SAS. All rights reserved. doi:10.1016/j.solidstatesciences.2005.07.003