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Rajamani Raghunathan Solid State and Structural Chemistry Unit, Indian Institute of Science, Bangalore-560012, India

Ranjith Ramaduraia) Department of Materials Science and Metallurgical Engineering, Indian Institute of Technology Hyderabad, Hyderabad 502205, Telangana, India

Adrian David and Wilfrid Prellier Laboratoire CRISMAT, ENSICAEN/CNRS, Caen 14050, France (Received 3 October 2016; accepted 27 December 2016)

YCrO3 (YCO) perovskite has been originally reported to be a biferroic with antiferromagnetic and ferroelectric (FE) properties, in which the origin of FE in YCO remains ambiguous. However, further studies reveal the presence of a global orthorhombic Pnma structure with a local structural heterogeneity. In this study, we discuss the high temperature phonon modes and their inter-relation to local structural distortions in YCO perovskite through Raman spectroscopy experiments and density functional theory (DFT) calculations. We observe that the Raman active B3g(3) out of phase scissor mode (SM) disappears above the dielectric transition temperature (Tc) commensurate with the local structural distortions. DFT calculations show that the transformation of a room temperature Y-cation distorted orthorhombic structure to a perfect orthorhombic structure above the dielectric transition temperature in which the Y cation is undisplaced could lead to the conversion of SM with symmetry B3g to Raman inactive B1u mode. I. INTRODUCTION

Rare-earth based chromite perovskites RCrO3 (R 5 Y or La to Lu) are widely studied for the interesting fundamental science they offer and applications in various fields such as interconnect of solid oxide fuel cells,1–3 humidity sensors,4 and negative temperature coefficient thermistors.5 Several investigations on orthochromites reveal weak multiferroic (ferroelectric (FE) and weak ferromagnetic) features whose FE transition ranges from 470 to 523 K and magnetic order transition ranges from 115 to 290 K.6,7 The FE features in these chromites are expected to arise due to the local structural distortions present in the structure which break the spatial inversion symmetry and create a polar order.8 Rajeswaran et al.9 showed that the presence of magnetic rare earth ion (R 5 Sm, Tm, Gd, and Er) and weak ferromagnetic nature (weak ferromagnetic interaction between R–Cr and antiferromagnetic interactions between Cr–Cr) of ‘Cr’ below Neel transition temperature could plausibly break the local symmetry and create a polar order in these materials.

Contributing Editor: Scott T. Misture a) Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2017.5

However, experimental investigations on certain nonmagnetic ions (R 5 Y or Bi or La) in the A-site orthochromites could also induce structural distortions giving rise to spin-phonon coupling below Neel temperature.10,11 Investigations on YCrO3 (YCO) reveal that it possesses a room temperature orthorhombic crystal structure with a FE Curie temperature (TC) of 473 K and an antiferromagnetic transition temperature of (Neel