High Temperature Phonon Emissivity of Simpler Manganites

N. E. MASSA; D. DE SOUSA MENESES; L. DEL CAMPO; P. ECHEGUT; J. A. ALONSO,

Orléans

Congreso; 15th International IUPAC Conference on High Temperature Materials Chemistry; 2016

IUPAC -Organiziing Committe

High temperature emissivity, the ratio of sample to black body?s luminescence, allows at CEMHTI measurements of far-infrared excitations complementing lower temperature reflectivity. Here we comment on spectra of ErMnO3 prepared in its rare earth ion size allowed orthorhombic metastable and hexagonal phases, ErMnO3 room temperature orthorhombic D2h16 (Z=4) changes to the highest temperature cubic topology mirroring NdMnO3.[1] The 300 K infrared phonons gradually decrease on heating as we approach the temperature of orbital disorder starting at ~1338 K. Adding to the understanding of lower temperature magnetoelectric couplings and phonon anharmonicities, the orthorhombic O´ lower temperature cooperative phase coexists with the cubic orthorhombic O up to ~1695 K. Above this, the three infrared active phonons coincide with the expected for cubic Pm-3m (Z=1) in the high temperature insulating regime. On the other hand, non-perovskite room temperature hexagonal ErMnO3 becomes on heating from polar at TC (ferroelectric) ~525 K to non-polar at TNP (antiferroelectric) ~1600 K. At ~1983 K, as in hexagonal TmMnO3 [2], the number of vibrational features is lower than predicted for centrosymmetric D6h4 (Z=2). We will also comment on spectral drawbacks when heating oxides in dry atmospheric air. [1] N. E. Massa, L. del Campo, D. de Sousa Meneses, P. Echegut, M. J. Martínez-Lope, and J. A. Alonso, J. of Phys. Cond. Matter 25 235603 (2013). [2] N. E. Massa, L. del Campo, D. De Sousa Meneses, P. Echegut, M. J. Martínez-Lope, and J. A. Alonso, J. of Phys. Cond. Matter 28 275901 (2014).