DSpace at VNU: Making room-temperature ferromagnetism in lead-free ferroelectric Bi0.5Na0.5TiO3 material

Author’s Accepted Manuscript Making room-temperature ferromagnetism in leadfree ferroelectric Bi0.5Na0.5TiO3 material L.T.H Thanh, N.B Doan, L.H Bac, D.V Thiet, S Cho, P.Q Bao, D.D Dung www.elsevier.com PII: DOI: Reference: S0167-577X(16)31566-X http://dx.doi.org/10.1016/j.matlet.2016.09.105 MLBLUE21543 To appear in: Materials Letters Received date: June 2016 Revised date: September 2016 Accepted date: 25 September 2016 Cite this article as: L.T.H Thanh, N.B Doan, L.H Bac, D.V Thiet, S Cho, P.Q Bao and D.D Dung, Making room-temperature ferromagnetism in lead-free ferroelectric Bi0.5Na0.5TiO3 material, Materials Letters, http://dx.doi.org/10.1016/j.matlet.2016.09.105 This is a PDF file of an unedited manuscript that has been accepted for publication As a service to our customers we are providing this early version of the manuscript The manuscript will undergo copyediting, typesetting, and review of the resulting galley proof before it is published in its final citable form Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain Making room-temperature ferromagnetism in lead-free ferroelectric Bi0.5Na0.5TiO3 material L T H Thanh1,4, N B Doan2, L H Bac1, D V Thiet1,3, S Cho3, P Q Bao4, and D D Dung1,* School of Engineering Physics, Ha Noi University of Science and Technology, Dai Co Viet road, Ha Noi, Viet Nam CNRS, Institut Néel, F-38042 Grenoble, France and Univ Grenoble Alpes, Institut Néel, F-38042 Grenoble, France Department of Physics, University of Ulsan, Ulsan 680-749, Republish of Korea Faculty of Physics, College of Science, Hanoi National University, 334 Nguyen Trai road, Ha Noi, Viet Nam Abstract We have successfully fabricated Mn-doped wide band gap lead-free ferroelectric Bi0.5Na0.5TiO3 by sol-gel technique The band gap reduced from 3.12 eV to 1.71 eV as increasing doping Mn concentration level up to mol% The room temperature ferromagnetism in Mn-doped Bi0.5Na0.5TiO3 samples was observed The magnetic moment was around 2.69 B/Mn at K We expected that this work will open the new direction for advance function of lead-free ferroelectric materials Key words: Sol-gel preparation; Lead-free ferroelectric; Ferromagnetism; Multiferroics; Perovskites Corresponding e-mail: *)dung.dangduc@hust.edu.vn I Introduction The research on mutiferroic materials is rapid development because it exhibits to create a new type of memory devices based on the combination of ferromagnetism and ferroelectricity in one material [1, 2] However, the multiferroic materials are rare to exist in nature because the conditions for being simultaneously ferroelectric and ferromagnetic are difficult to achieve due to the usual atomic-level mechanism [3, 4] Therefore, it remains a major challenge to obtain new multiferroic materials at room temperature The most recently development the mutliferroic materials based on the lead-based piezoelectric materials because it was promised to create the new general function from traditional lead-based ferroelectric materials in multiferroic technology [5-7] Note that the lead-based ferroelectric materials were still present 94.5% of the market in 2014 even the material have districted because it contained more than 60 wt% Pb which are pollution environment and harmful to human [8] Therefore, environmental issues have raised the need for non-hazardous materials for use in device fabrication Thus, considerable effort has been devoted towards the development of lead-free multiferroic materials Among lead-free ferroelectric materials, the alkali-based ferroelectric materials Bi0.5A0.5TiO3 (A=Na and K) have been widely studied because of the competitive properties to Pb(Zr,Ti)O3-based materials [9] Therefore, influence of room temperature ferromagnetism in lead-free ferroelectric materials is possible channel to create the new general devices The room temperature ferromagnetism is reported for transition metal such as Co doped Bi0.5Na0.5TiO3 or Fe-doped Bi0.5K0.5TiO3 nanocrystal [10, 11] In this work, the room temperature ferromagnetism was observed for Mn-doped Bi0.5Na0.5TiO3 nanocrystal The saturation magnetization was around 2.69 B/Mn at 5K The reduction of band gap optical, from 3.12 eV for un-doped to 1.71 eV for mol% Mn-doped Bi0.5Na0.5TiO3, was obtained due to the presence of Mn ions in the Ti site II Experiment The lead-free ferroelectric Bi0.5Na0.5TiO3 (named as BNT) and Mn-doped Bi0.5Na0.5TiO3 (named as BNT-xMn with x = 0.5, 1, 3, 5, and 9) samples were synthesized by the solgel technique The experimental process and characterization was described in details in Ref [11] The sodium was added to excess around 20 mol% to prevent the sodium loss during gel and sintering process The vibrational and rotational modes in samples were characterized by Raman spectroscopy III Results and discussions Fig.1 (a) shows the x-ray diffraction (XRD) patterns of pure and Mn-doped Bi0.5Na0.5TiO3 samples All samples show single phase with perovskite structure A comparison on the location of (003) diffraction peaks in the range of 45.5-48.5 shows that the peaks position of the Mn-doped samples shifts toward a higher 2 values (Fig (b)), indicated that Mn incorporated with lattice structure Based on the Shannon reported, the ionic radii of Mn2+, Mn3+, Mn4+ and Ti4+ with six coordination are 0.83, 0.645, 0.53 and 0.605Å, respectively [12] The Mn states were reported from Mn2+ to Mn4+ which is depending on specially the materials and fabrication processing [13, 14] Therefore, the present of valence state of ions Mn resulted in influence of distortion on lattice parameter which are very complicated Our results indicated that the peaks position shiftted to higher 2 values for doped samples; therefore, we suggest that the average ionic radius of Mn dopant is smaller than that of ionic Ti4+ Fig.2(a) shows the Raman spectra of pure Bi0.5Na0.5TiO3 and Mn-doped Bi0.5Na0.5TiO3 in the wave number range of 100-700 cm-1 The Raman spectra were relatively broad which resulted from disorder on the A-site and from overlapping Raman modes The effect of Mn ion substitution for Ti on the phonon vibration (Fig 2(b)), where the high magnification Raman spectra of un-doped and Mn-doped Bi0.5Na0.5TiO3 in the wave number range of 150450 cm-1 The vibration modes for Bi0.5Na0.5TiO3 in the range of 109-134 cm-1 are dominated by displacement of Bi ions, and the modes in the frequency range of 155-187 cm-1 and 246401 cm-1 are dominated by Na-O and TiO6 vibrations, respectively, while the modes in the range 413-826 cm-1 are primarily associated with the oxygen octahedral [15] The result indicated that the Ti-O bands shifted to lower frequency as the Mn concentration increased The change frequencies of Raman spectroscopy in Mn-doped Bi0.5Na0.5TiO3 at Ti-O band is solid evidence of Mn substitution at Ti site cause of the higher mass of the Mn ion compared with Ti ions Fig 3(a) shows the optical absorption spectra of Bi0.5Na0.5TiO3 and Mn-doped Bi0.5Na0.5TiO3 samples The appearance of multi absorbance peaks (e.g around 426 and 620 nm) suggested for multi local states of Mn ion in forbiddance gap of Bi0.5Na0.5TiO3 materials The band gap (Eg) values reduced from 3.12 eV to 1.71 eV for un-doped and mol% Mn-doped Bi0.5Na0.5TiO3, respectively (Fig 3(b)) Recently, theoretical calculation predicted that the Bi0.5Na0.5TiO3 compound has conduction band mostly contains Bi-6p, Ti-4s, Na-3s and Na2p orbitals and the bottom of the valence band is constructed from Bi-6s and O-2p orbitals [16] Our current work on Fe-doped Bi0.5K0.5TiO3 materials also indicated that the presence of conduction bands of Fe resulted in reduction of band gap [11] Thus, we suggested that the incorporation of Mn-d orbital electronics into the lattice reduced the band gap of Bi0.5Na0.5TiO3 materials, which result from the present of new states in electronic structure of both the highest occupied molecular orbital and lowest unoccupied molecular orbital associated with the presence of Mn stabilized by an accompanying O-vacancy (Fig 3(c)) Therefore, we suggested that the reduction of band gap in transition metal doped lead-free ferroelectric materials results from contribution of conduction bands of transition metal in total density of state of lead-free ferroelectric materials Figure 4(a) shows the magnetic hysteresis (M-H) loops of the undoped and Mn-doped Bi0.5Na0.5TiO3 samples at room temperatures The anti-S-shape is observed for undoped samples resulting from the competion between ferromagnetic and diamagnetic The origin of weak-ferromagnetism at room temperature of un-doped samples was predicted from vacancyinduced magnetism via ab initio calculation [17] By the incorporation of Mn in Bi0.5Na0.5TiO3 lattice, the weak diamagnetic signal has been converted to a feeble ferromagnetic loop confirming ferromagnetism at room temperature The coercive field and remanence magnetization were around 80 Oe and 0.5 memu/g, respectively, which were solidly evident for ferromagnetism behavior at room temperature However, the unsaturation of magnetization was obtained in M-H curve for Mn concentration added Bi0.5Na0.5TiO3 over mol% which resulted from compensation of ferromagnetic and paramagnetic of exchange interaction between magnetic ions and isolate magnetic ion in host lattice, respectively [10, 11] Fig 4(b) shows the dependence of magnetization on temperature under an applied field of kOe of Bi0.5Na0.5Ti0.99Mn0.01O3 samples The inset of Fig 4(b) shows the M-H curve of Bi0.5Na0.5Ti0.99Mn0.01O3 samples under magnetic up to 70 kOe at various temperatures The maximum magnetization was ~0.71 emu/g at K which was corresponded to 2.69 B/Mn Therefore, we suggested that present of room temperature ferromagnetism in Mn-doped Bi0.5Na0.5TiO3 was possible due to exchange splitting of transition metal at octahedral site and/or enhancement via oxygen vacancies IV Conclusion The room temperature ferromagnetism was obtained in Mn-doped Bi0.5Na0.5TiO3 materials The magnetic moment was around 2.69 B/Mn at K The reduction of band gap values from 3.12 eV to 1.71 eV resulted from substitution of Mn at Ti-octahedral sites We expected that this work will show an advance function of lead-free ferroelectric materials Acknowledgment This research is funded by Vietnam National Foundation for Science and Technology Development (NAFOSTED) under Grant number 103.02-2015.89 Figure captions Fig 1(a) XRD pattern of Mn-doped Bi0.5Na0.5TiO3 as a function of Mn doping concentration and (b) a comparison of (003) diffraction peak positions in 2 range of 45.5-48.5 Fig 2(a) Raman spectra of Mn-doped Bi0.5Na0.5TiO3 as a function of Mn doping concentration, and (b) a magnification of wave positions in range of 150-400 cm-1 Fig 3(a) UV–vis absorption spectra and (b) the dependence of (αhν)2 on photon energy (hν) of the pure and Mn-doped Bi0.5Na0.5TiO3 samples (c) Schematic illustration of mechanism for band-gap narrowing in the transition metal doped lead-free Bi0.5Na0.5TiO3 materials Fig 4(a) M–H curves of the Bi0.5Na0.5TiO3 and Mn-doped Bi0.5Na0.5TiO3 samples, and (b) The M–T curve at kOe magnetic field for Bi0.5Na0.5Ti0.99Mn0.01O3 samples The inset of Fig 4(b) shows M–H curve of Bi0.5Na0.5Ti0.99Mn0.01O3 samples at K References [1] T Kimura, T Goto, H Shintani, K Ishizaka, T Arima, and Y Tokura, Nature 426 (2003) 55-58 [2] N Hur, S Park, P A Sharma, J S Ahn, S Guha, and S W Cheong, Nature 429 (2004) 392-395 [3] N A Spaldin, and M Fiebig, Science 309 (2005) 391-392 [4] N A Hill, J Phys Chem B 104 (2000) 6694-6709 [5] L M Oanh, D B Do, N D Phu, N T P Mai, and N V Minh, IEEE Trans Magn 50 (2014) 2502004 [6] B Y Wang, H T Wang, S B Singh et al., RSC Adv (2013) 7884-7893 [7] M Murakami, K S Chang, M.A Aronova, C L Lin, M H Yu, J H Simpers, M Wuttig, and I Takeuchi, Appl Phys Lett 87 (2005) 112901 [8] W Jo, R Dittmer, M Acosta, J Zang, C Groh, E Sapper, K Wang, and J Rodel, 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were synthesized by sol–gel method - Mn-doped Bi0.5Na0.5TiO3 exhibited room temperature ferromagnetism - The reduction of band gap from 3.12 to 1.71 eV was obtained - A new function of lead-free ferroelectric materials is proposed 12 .. .Making room-temperature ferromagnetism in lead-free ferroelectric Bi0.5Na0.5TiO3 material L T H Thanh1,4, N B Doan2, L H Bac1, D V Thiet1,3, S Cho3, P Q Bao4, and D D Dung1,* School of Engineering... combination of ferromagnetism and ferroelectricity in one material [1, 2] However, the multiferroic materials are rare to exist in nature because the conditions for being simultaneously ferroelectric. .. non-hazardous materials for use in device fabrication Thus, considerable effort has been devoted towards the development of lead-free multiferroic materials Among lead-free ferroelectric materials,