RESEARCH ARTICLE DOI: xxxxxxxxxxxxx

Phase Transition of La0.62Sr0.38MnO3 Perovskite Manganites

K. Sakthipandia* and M. Selvamb

Department of Physics, Sethu Institute of Technology. Kariapatti 626 115, Tamil Nadu, India

Centre for Nano Science and Technology, K S Rangasamy College of Technology, Tiruchengode 637215, Tamil Nadu, India

*Corresponding Author

sakthipandi@gmail.com

(Sakthipandi K)

Received	: XX-XX-XXXX

Accepted	: XX-XX-XXXX

ABSTRACT: Bulk and nano La0.62Sr0.38MnO3 perovskite manganite samples were prepared using solid state and sonochemical reaction respectively. The ultrasonic velocities measurement was made on prepared samples using ultrasonic through transmission method, at a fundamental frequency of 5 MHz over wide range of temperatures. The temperature dependence of the ultrasonic parameters shows an interesting anomaly in bulk and nano perovskite samples. The observed dramatic softening and hardening in sound velocities are related to phase transitions. Further, a decrease in grain size in the nanostructured sample leads to a shift in the ferromagnetic transition temperature (TC) from 375 to 370 K.

Keywords: Perovskite, Ultrasonic velocity, Grain size, Curie temperature

1. Introduction

In the past few years, perovskite manganites R1-xAxMnO3 (where R trivalent rare earth elements and A divalent alkaline earth ions) were attracted for potential applications like solid oxide fuel cells, magnetic sensors/reading heads and frequency switching devices due to their unique physico-chemical [1-3], and giant magneto resistance (GMR) properties [4]. In perovskite magnetic materials, particularly La0.68Sr0.32MnO3 (LSMO) perovskite, the existence of highest value of Curie temperature (TC) and very low carrier density with a high spin polarisation of charge carriers make them very promising candidate for room temperature applications. The nanostructured materials are used to widen the opportunities to improve the catalytic activity in solid fuel cells [3]. Generally, the properties of the doped perovskite materials depend on (i) doping concentration (x) [5], (ii) ionic size of A site divalent cation [6], (iii) the variation of doped ions and potential fluctuations between R3+ and A2+ [7] and (iv) phase separation [8]. Therefore, in the present investigation, an attempt has been made to prepare bulk and nanocrystalline LSMO perovskite magnetic materials and to study the structural and phase transitions employing on-line ultrasonic velocity measurements.

2. Experimental procedure

Bulk and nano La0.68Sr0.32MnO3 perovskite manganites were prepared employing respectively solid state and sonochemical reaction methods. The characterisation of prepared samples was made by studies such as X-ray diffraction (XRD), Transmission electron microscope (TEM) and on-line ultrasonic measurements [4, 9].

3. Result and Discussion

The XRD patterns of bulk and nano LSMO perovskite samples are shown in Figure 1. It is inferred that the observed XRD patterns of the bulk sample reveals the existence of mixed crystalline nature namely rhombohedral and tetragonal crystalline phases. The peaks observed at 27.616º and 48.365º correspond to tetragonal phase and other peaks correspond to rhombohedra phase (JCPDS file no.: 89-4461 and 51-0118). On the other hand, rhombohedra phase with the space group of R3c along with the hexagonal structure (JCPDS file no.: 51-0409) is observed in the nano LSMO perovskite. The TEM images of bulk and nano samples are shown in Figure 2. Interestingly, bulk LSMO perovskite samples have sphere like morphology, whereas nano LSMO perovskite samples have honeycomb structure consisting of agglomerated nanoparticles with particle sizes ranging from 30 to 50 nm. The estimated

Fig. 1. XRD pattern of a) bulk and b) nano LSMO perovskites

Fig. 2. TEM patterns of a) bulk and b) nano LSMO perovskites

Fig. 3. Temperature dependent relative change in longitudinal velocity of bulk and nano samples

particle size from TEM studies is around 500 nm for bulk and 50 nm for nano LSMO perovskite. The temperature dependence of percentage variation in longitudinal (UL) and shear (US) velocities of bulk and nano sample are represented respectively in Figure 3. A gradual decrease in velocity and an increase in attenuation are observed in the temperature range 300 to 370 K and 380 to 500 K as observed in other solid material [4]. An anomalous behaviour is noticed at 375 K for bulk sample. The observed sharp dip in velocity and a peak in attenuation at 375 K in bulk sample is the Curie

Fig. 4. Temperature dependent relative change in shear velocity of bulk and nano samples

temperature (TC) of LSMO perovskite wherein a transition from ferromagnetic to paramagnetic takes place [4, 10]. In nano samples, an initial monotonic decrease in velocities and an increase in attenuation are observed in the temperature range from 300 to 355 K.

Nevertheless, it is interesting to note an anomalous behaviour in the variation of velocities and attenuation in the temperature range from 355 to 385 K. A sharp fall in velocities and a sharp increase in attenuation start at 355 K and reach the maxima/minima in their variation at 370 K. A further increase in temperature beyond 370 K leads to a sharp rise in velocities and a sharp decrease in attenuation up to 385 K. Beyond 385 K, a monotonic decrease in velocities and an increase in attenuations are noticed. The shift in the peak from 375 to 370 K indicates that the TC for the perovskite materials is shifted towards the lower value due to the decrease in grain size. Further, the observed broad variation in velocity at TC in nano sample than the bulk sample conforms the absence of sharp FM to PMM transition, as reported [4, 11]. The linear magnetostriction effect is more dominate in LSMO perovskite than volume magnetostriction effect which is evident from larger variation in both velocities (UL and US).

Reference

G. Lalitha, D. Das, D. Bahadur, and P. Venugopal Reddy, Elastic behavior of La0. 67Ca0.33MnO3: ZrO2 composites, J Alloy Compd., 464 (2008) 6-8.

W. J. Li, Bo Zhang, and W. Lu, Structural properties and Raman spectroscopy of La (2+ 4x)/3Sr(1− 4x)/3Mn1− xCuxO3 (0⩽ x⩽ 0.2), Phys Lett A. 362 (2007) 327-330.

P.Sarkar, P. Mandal, A.K. Bera, S.M. Yusuf, L.S. Sharath Chandra, and V. Ganesan, Field-induced first-order to second-order magnetic phase transition in Sm0.52Sr0.48MnO3, Phys. Rev. B., 78 (2008) 012415.

S. Sankarrajan, K. Sakthipandi, and V. Rajendran, Temperature-dependent sound velocities, attenuation and elastic moduli anomalies in Pr1−xSrxMnO3 perovskite manganite materials at 0.28≤ X≤ 0.41, Phase Transitions, 85 (2012) 427-443.

A. Urushibara, Y. Moritomo, T. Arima, A. Asamitsu, G. Kido, and Y. Tokura, Insulator-metal transition and giant magnetoresistance in La1-xSrxMnO3, Phys. Rev. B, 51, (1995) 14103.

H.Y. Hwang, S.W. Cheong, P.G. Radaelli, M. Marezio and B. Batlog, Lattice Effects on the magnetoresistance in doped LaMnO3, Phy. Rev. Lett., 75 (1995) 914.

M. Lide, J. Rodriguez Martinez and J. Paul Attfield, Cation disorder and size effects in magnetoresistive manganese oxide perovskites, Phys. Rev.B, 54 (1996) R15622.

M. Uehara, S. Mori, C.H. Chen and S.W. Cheong, Percolative phase separation underlies colossal magnetoresistance in mixed-valant manganites, Nature, 399 (1999) 560-563.

M. Arunachalam, P. Thamilmaran, S. Sankarrajan, and K. Sakthipandi, Study of high temperature metal-insulator phase transition in La1−xCaxMnO3 employing in-situ ultrasonic studies, Physica B: Condensed Matter, 456 (2015) 118-124.

K. Sakthipandi and V. Rajendran, On-line phase transitions of bulk and nanocrystalline La1− xPbxMnO3 (x= 0.3, 0.4, and 0.5) perovskite manganite materials using ultrasonic measurements, Mater. Chem. Phys., 138 (2013) 581-592.

R.K. Zheng, C.F. Shu, J.Q. Xie, R.X. Huang and X.G. Li, Charge transport and ultrasonic properties in La0.57Ca0.43MnO3 perovskites, Mater. Chem. Phys., 75 (2002) 121-124.

Author Biography

K. Sakthipandi was born in Tirumangalam, Madurai, India, in 1982. K. Sakthipandi completed his under graduation with distinction in the field of Physics at The American College, Madurai and he got the post-graduationfrom School of Physics, Madurai Kamaraj University, Madurai along with Maveeran Sundaralingam Award for higher number of marks scored in II M.Sc. Physics for the year 2004-2005. He obtained his PhD in Physics with highly commended from Anna University, Chennai. He received the Dr. TK Saxsena Memorial Award from Ultrasonic Society of India for the best thesis entitled “On-line Ultrasonic Characterization of Bulk and Nano Perovskites and Maraging Steel” in the field of Ultrasonics. He started his carrier as a Lecturer in Physics at Erode Arts College, Erode in 2005. He worked as a Lecturer in Physics at KSR College of Technology in 2007. Later in 2008, he joined as a Junior Research Fellow in IGCAR sponsored project and doing the research on material characterization. He got the Senior Research Fellowship (SRF) in 2011 and the Extended SRF in 2013 from Council of Scientific and Industrial Research (CSIR), New Delhi. He has published more than 52 research papers in peer reviewed international journals and he presented his work more than 85 national/international conferences. He has received many laurels and awards such as, Student Visiting Research Fellowship from Indian Academy of Science, Young Scientist Visiting Fellowship from Tamil Nadu State Council for Science and Technology, Chennai, Visiting Research Scientist Fellowship from Indian National Science Academy, International Student Fellowship Award from Acoustical Society of America (ASA), Best Research Paper Award on Structural Acoustics from Madras India Regional Chapter – ASA, Best oral presentation Award from Acoustical Society of India, Best Poster Presentation Award from Material Research Society of India, Mumbai Chapter and Best Paper Award in the field of Physical Acoustics from Acoustical Society of India. In addition to, he got the Research Projects from various funding agency such as, DST Fast-Track for the entitled of “Synthesis and Characterization of Polymer blended lanthanides doped nano ferrites” and IITB-INUP for the entitled of “Correlation of Temperature-dependence Ultrasonic Parameters with Magnetic measurements”. He is actively participated as a reviewer in Journal of Alloys and Compound, Phase Transitions, Journal of Non-destructive Testing and Evaluation, Materials Research Bulletin and Materials Chemistry & Physics.

M. Selvam was born in Cuddalore, Tamil Nadu, India on July 12th 1985. M. Selvam completed his undergraduate with distinction in the field of Industrial Chemistry at Periyar Arts College, University of Madras, Chennai on 2005 and completed his post graduate with distinction in the fields of industrial chemistry (Electrochemistry) at Alagappa University, Karaikudi, Tamil Nadu on 2007. He was ranked first in his undergraduate B.Sc., and postgraduate M.Sc. degree with the honour of gold medal from the universities. He obtained his Ph.D in chemistry for the title “Synthesis and Characterization of Carbon based Nano materials for electrochemical device applications” by Anna University, Chennai. He started his carrier in 2005 as a Technical Lab Assistant in Environmental Impact Monitoring of Sethu Samuthuram Ship Channel Project (Chemical Parameters) & ECR-TNRSP-O4 Project. Then he worked as a lab technician in Sterilite Industries, Tutocorin. In 2010 he joined as a Junior Research Fellow at Center for Nano Science & Technology, K.S.Rangasamy College of Technology, Erode. He got his Senior Research Fellow in 2014 at Center for Nano Science & Technology, K.S.Rangasamy College of Technology. He received INSPIRE fellowship as a researcher for the year of 2011, by Department of Science and Technology (DST), New Delhi. He has published more than 25 Papers in reputed international journal and and he presented his work more than 60 national/international conferences. He has received many laurels and awards. He has been as an organizing member for five international and 15 national conferences. He has done various electrochemical studies with graphene and its allied family elements. He is a pioneer in synthesis of carbon nanomaterials. Determined to eventually work hard and optimistic, he has worked in various projects related to nanomaterials.