Vibration Spectroscopy Study of Ferroelastoelectric [(CH3)2CHNH3]4Cd3Cl10 Doped with Copper

V. Kapustianyka, Yu. Chorniia, V. Rudykb, Z. Czaplac, R. Cachc, O. Kolomysd, B. Tsykaniukd aSolid State Physics Chair, Ivan Franko National University of Lviv, Dragomanova str. 50, 79005 Lviv, Ukraine bScientific-Technical and Educational Center of Low-Temperature Studies, Ivan Franko National University of Lviv, Dragomanova str. 50, 79005 Lviv, Ukraine cInstitute of Experimental Physics, University of Wrocław, pl. M. Borna 9, 50204 Wrocław, Poland dV.E. Lashkaryov Institute of Semiconductor Physics NAS of Ukraine, pr. Nauki, 41, 03028 Kyiv, Ukraine

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Infrared absorption spectra of [(CH3)2CHNH3]4Cd2Cl10:Cu crystals with copper concentration of 0.6±0.1% and 1.8±0.1% were investigated in the spectral range of 30-12000 cm-1 and Raman spectra of the same crystals were investigated within the range of 30-4000 cm-1. These crystals belong to a large family of compounds with the metal-halogen polyhedra of different types manifesting various phase transitions including those into the ferroelectric, ferroelastic and even ferroelastoelectric phases. The related crystals with an alkylammonium cation and transition metal ions in their structure were found to be multiferroics since they are characterized by the coexistence of ferroelectric and magnetic ordering. The obtained data for [(CH3)2CHNH3]4Cd2Cl10:Cu crystals were compared with those for the initial compound without copper. Increasing the Cu2+ concentration in the crystals leads to merging of bands in the infrared spectra corresponding to the skeletal vibrations of IPA cations because of their interaction with the complex anions consisting of two types of octahedra: CdCl6 and CuCl6. Moreover, for all investigated crystals and geometries of experiment a considerable splitting of the Raman modes corresponding to skeletal vibrations of IPA cation and asymmetric stretching vibrations of the methyl groups were observed. This case corresponds to Davydov's splitting connected with the presence of different numbers of distinct IPA cations. A very similar character and level of the mentioned splitting testifies to the fact that the crystals doped with copper are characterized by the same structure of phase II as the initial IPACC crystal. The doped crystals with a higher concentration of Cu2+ manifest very broad bands in the region above 9000 cm-1 which would be related to the intra-ion transitions in Cu2+ ion. The performed analysis of the IR and Raman spectra both of the initial crystals and those doped with copper allowed to identify more precisely the real phonons which are most of all involved in the formation of the absorption edge.

DOI:10.12693/APhysPolA.138.488 topics: multiferroics, infrared spectra, Raman spectra, ferroelastoelectric