Z. Kristallogr. Suppl. 27 (2008) 205-210 / DOI 10.1524/zksu.2008.0026 205 © by Oldenbourg Wissenschaftsverlag, München Structural state of Eu 2 (MoO 4 ) 3 single crystal after different thermobaric treatments E. A. Kudrenko 1,* , I. M. Shmyt’ko 1 , V. V. Sinitsyn 1 , E. G. Ponyatovsky 1 , B. N. Red’kin 1 1 Institute of Solid State Physics RAS, Chernogolovka, Moscow district 142432, Russia * lenak@issp.ac.ru. Keywords: rare-earth compounds, high-pressure amorphization, X-ray diffraction, dilatome- try study Abstract.The X-ray and dilatometric studies of Eu 2 (MoO 4 ) 3 single crystal after different thermobaric treatments were carried out. The compression of the initial -phase of Eu 2 (MoO 4 ) 3 single crystal to P=9 GPa at room temperature results in new high-pressure phase (hpp) formation which is retained at decompression to P=1 atm. The hpp phase under- goes phase transition back into  phase around T=860-880 K at heating. The hpp– phase transition is accompanied by the unusual structure state formation when coherent reflections are essentially dropped and all x-ray diffraction intensity of the sample is transformed into the background-like spectrum. 1. Introduction Solid state amorphization (SSA) under pressure is actively studied last decades [1-3]. It was found more hundred substances which undergo SSA and some of them remain in the amor- phous state at the releasing pressure to 1 atm. These investigations have been usually per- formed on the polycrystalline samples at the quasihydrostatic conditions whereas only a few works were devoted to SSA studies both on polycrystalline and single crystal samples. Par- ticularly unexpected results were found at investigations of AlPO 4 (berlinite) single crystal which became amorphous at pressures ~ 15 GPa but transformed back into a single crystal state with the same orientation (memory-glass effect) at decompression to 1 atm [4,5]. Recently the quite similar results were found for Eu 2 (MoO 4 ) 3 [6]. The thermodynamically stable phase of the crystals at ambient conditions is the monoclinic α–phase, which usually is not formed by traditional methods and samples are in metastable tetragonal β -phase [7]. The high pressure investigations of polycrystalline β–Eu 2 (MoO 4 ) 3 using both “in situ” and thermobaric treatments methods revealed amorphization in the compound at P≈7-9 GPa [8- 11]. The amorphous state was retained after releasing pressure to 1 atm and transformed back into crystalline β–phase only at sample heating to ~723 K.