Supporting Information

Transcription

1 Supporting Information Room Temperature Magnetodielectric Effect in La γ ; rigin and Impact of Excess xygen Hari Mohan Rai a)1, Preetam Singh a)1 Shailendra K. Saxena 1, Vikash Mishra 1, M. Kamal Warshi 1, Rajesh Kumar 1, Parasmani Rajput 2, Archna Sagdeo 3, Indrani Choudhuri 4, Biswarup Pathak 4 and Pankaj R. Sagdeo 1* a) Authors having equal contribution prs@iiti.ac.in 1 Material Research Lab. (MRL), Department of Physics and MSE; Indian Institute of Technology Indore, Khandwa road, Simrol, Indore (M.P.) , India. 2 Atomic& Molecular Physics Division, Bhabha Atomic research Centre, Mumbai , India 3 Raja Ramanna Center for Advance Technology (RRCAT), Indore, M.P , India 4 Discipline of Chemistry, School of Basic Sciences Indian Institute of Technology (IIT) Indore, Khandwa road, Simrol, Indore (M.P.) , India S1

2 FIGURE-S1: The three dimensional crystallographic refined crystal structure of La 3. Each ion is surrounded by six oxygen ions and hence a 6 octahedral structure is formed around each ion. Here, the biggest blue balls are La ions, medium size pink balls are ions whereas the smallest red balls are oxygen ions. FIGURE-S2: Three dimensional symmetric illustration of the refined crystal structure of La as a representative case for presently studied LGF (La 1-x x 3 ) samples with 0 x 0.4. The structure is demonstrating (/) 6 octahedra as each / ion is surrounded by 6 oxygen ions. Each La ion is surrounded with 8 oxygen ions. Blue large sphere represents La ions, medium size green flagged pink sphere represents / ions and small red sphere shows ions. The corresponding values of refined parameters for all studies samples are listed in following tables. S2

3 The crystal structures shown in Figure S1 and S2 of un-doped and doped LG are developed through Vesta software by using the crystal information file from Rietveld refinements. The structure belongs to orthorhombic symmetry with Pnma space group. In that pnma structure, the corresponding positions of all cations (La and /) and anions () are tabulated in the following table S2. The XRD pattern of LGF (La 1-x x 3 ) samples with 0 x 0.4 reveals no structural phase transition from orthorhombic to any other phase. The / atoms are octahedrally coordinated by atoms as shown in Figure S1 and S2. TABLE S1: Parameters,which decide the quality of fitting and refinement, are tabulated for all presently studied LGF (La 1-x x 3 ) samples i.e. with 0 x 0.4. La 1-x x 3 (LGF) χ 2 (Chi 2 ) Brag R- Factor R-F Factor X= X= X= X= X= TABLE S2: Refined atomic positions for Pnma phase of presently studied LGF (La 1- x x 3 ) samples with x=0.0 to x=0.4. La / 1 2 LGF (4c) (4a) (8d) (4c) samples x, y, z x, y, z x, y, z x, y, z X = , 1/4, , 0, , , , 1/4, X = , 1/4, , 0, , , , 1/4, X = , 1/4, , 0, , , , 1/4, X = , 1/4, , 0, , , , 1/4, X = , 1/4, , 0, , , , 1/4, TABLE S3: Refined lattice parameters for LGF (La 1-x x 3 ) samples with 0 x 0.4. LGF samples a (Å) b (Å) c (Å) X = X = X = X = X = S3

4 TABLE S4: Refined bond angles determined through Vesta software by using refined structure for presently studied LGF (La 1-x x 3 ) samples with x=0.0 to x=0.4. Bond Angles (degree) La 1-x x 3 (LaD 3 ) Here, D=/ La- 1 -La D- 1 -D D- 2 -D X= (2) # 161.0(4) # 158.4(5) # X= (3) 163.1(4) 149.6(5) X= (3) 159.6(4) 157.5(5) X= (3) 159.5(4) 157.2(6) X= (3) 158.9(4) 160.1(6) # D= TABLE S5: Refined cation-anion distances determined through Vesta software by using refined structure for presently studied LGF (La 1-x x 3 ) samples with x=0.0 to x=0.4. La 1-x x 3 (LaD 3 ) Here, D=/ D- 1 D- 2 La- 1 La- 2 X= (17) # 1.942(17) # 2.655(17) # 2.788(15) # X= (14) 1.886(15) 2.260(17) 2.509(14) X= (12) 1.971(12) 2.607(11) 2.815(13) X= (14) 1.958(15) 2.600(11) 2.467(15) X= (17) 1.981(17) 2.599(11) 2.807(17) # D= The analysis of above observed results reveals that no such structural information is obtained which can be correlated directly with the observed MD phenomenon. In order to get a better view about the structural intrinsicality of presently observed MD phenomenon, we recommend to perform XRD, XANES and EXAFS (at k-edge), and Raman measurements in the presence of magnetic field which may enable to observe the magnetically induced structural changes (if taking place) at global and localized (around atom) level respectively. S4

5 FIGURE-S3: Room-temperature loss tangent (tanδ) as a function of frequency measured in the absence (H=0.0 T) and presence (H=0.2 T to 1.2 T) of magnetic field. The data is shown only for higher frequencies to demonstrate that the value of tanδ increases with increasing magnetic field even at the frequencies of > 1 MHz and its value remains <1 even at such high frequencies. Calculation for determining charge state and percentage of 3+ and 4+ in La γ by using the results of iodometric titration:- (i) Charge state (say x) For the present sample, by charge neutrality condition, La x 0.3 ( ) La x 0.3 (0.044) Here, x is the charge state of in present sample and γ = (by titration), Thus, ( 1) ( ).3x ( 3.044) x x x x 0.3 x 3.29 Thus, through iodometric titration, the charge state of in present sample is found S5

6 (ii) Percentage of 3+ and 4+ For the present sample, by charge neutrality condition, La La ( ) 0.3(1 x ) 0.3x ( ) Here, x is the amount of 4+ in the total present in the sample. Since, through titration experiment the value of γ is found to be 0.044, therefore, according to charge neutrality condition La 4 0.3(1 x) 0.3x ( ) La 0.3(1 x) ( 1) () [0.3(1 x )] (4 0.3x) ( 3.044) x 1.2x x x x 0.3 x x (0.044) Thus 4+ is 29% out of total present in the sample whereas remaining 71% is 3+. S6

7 XANES Analysis:- The obtained XANES data is plotted in following Figure S4. The energies corresponding to absorption edge of - pure metal foil ( 0 ) and powders of ( 2+ ) and 2 3 ( 3+ ) have been used as standards. The oxygen stoichiometry of powders (standards) has been validated through iodometric titration before using them as standards. It is notable that XANES measurements for La γ and also for all these standards are performed with same experimental settings at RT. FIGURE-S4: K-edge XANES spectra of La γ (LG7F3) with 2+ and 3+ standards. Since the absorption edge of -metal foil ( 0 ) appears at a relatively low energy side (7112 ev), therefore, to clearly visualise the relative shift in the position of LG7F3 absorption edge with (2 + and 3 + ), the XANES data of 0 is not shown. Inset shows K-edge energies as a function corresponding oxidation states of standards (i.e., 0, 2+ and 3+). Figure S4 compares the normalized XANES spectra of LGF (x=0.3) with 2+ and 3+ standards. The absorption edge (K-edge) energies of ( 2+ ), 2 3 ( 3+ ) and La γ are determined with the help of previous convention 1, by plotting the first derivative of the corresponding μ(e) versus E curves as shown in following Figure S5 for La γ and used standards. The value of energy corresponding to first maximum (exclude the one corresponding to pre-edge) on this first derivative curve gives the position of the inflection point and hence the position of the absorption edge 1. In this way, the calculated S7

8 FIGURE-S5: Estimation of absorption K-edge energy. The first derivative of µ(e) versus E curve for standards and La γ. For clarity the data of metal foil is shown separately in the inset. The energy coordinate of small circle indicates corresponding K-edge energy. K-edge energy of La γ is found to be greater than that of the 2 3 (3+) indicating coexistence of 3+ and 4+ in the sample. The estimated K-edge energies of sample and standards are summarized in following table S6. TABLE S6: K-edge absorption energies, for sample and standards i.e., metal foil ( 0 ), ( 2+ ) and 2 3 ( 3+ ), estimated through first order derivative of μ(e) versus E curves by means of XANES data (above Figure S4 and S5). Sample/standard K-edge energy (ev) metal foil ( 0 ) ( 2+ ) ( 3+ ) La γ In order to obtain a precise value of oxidation setae of in La γ, the calculated edge energies of ( 2+ ), 2 3 ( 3+ ) along with that of the metal foil ( 0 ) are then plotted as a function of corresponding charge states (i.e. 0, 2+ and 3+) as shown in the inset of above Figure S4. This data is then fitted with a 2 nd order polynomial 2,3 of the following form 2 y B1 x B2x Intercept Here, x represents charge state whereas y is the corresponding K-edge energy. Thus, to estimate the charge state of in La γ, the corresponding K-edge energy i.e., S8

9 y= ev (above Figure S5 or Table S6) along with the values of B1 (-8), B2 (7.26) and intercept (7112) as obtained from the table of fitting parameters, is substituted in above 2 polynomial i.e x 7.26x After solving this quadratic equation, the oxidation state of in La γ, is estimated between +3 and +4 (i.e. x ). This coexistence of 3+ and 4+ is attributed to oxygen off-stoichiometry (oxygen excess) in the sample. By using this value (3.29) in the following charge neutrality condition - La ( ) ( 1) () ( ) ( ) R R R the value of gamma (γ) is found to be which is closely consistent with that of the value (0.044) obtained through titration experiments. Hence, the charge state of and concentration of 3+ / 4+ in La γ sample calculated through both, XANES and titration experiments, are consistent with each other. S9

10 Identification of different frequency regions: Circuit Analysis of impedance data (Cole- Cole plot) :- In order to identify frequency segments corresponding to different contributions, Z - Z data obtained in the absence (H=0T) and presence (H=0.2T to H=1.2T) of magnetic field (Figure 6 (a) of main text), is fitted with the help of EIS (Electrochemical Impedance Spectroscopy) Spectrum Analyzer software by considering the circuit model shown in Figure 6 (b) of main text. The results obtained from this fitting are shown in the same Figure only for data (Z -Z ) corresponding to H=0.2T as a representative. The data is fitted over the entire range (shown in (Figure 6 (a) and 6 (b) of main text)) of probing frequency considering a series of three capacitors (each having a resistance in parallel individually). The first capacitor-cpe1 represents constant phase element. The contributions of grains, grain boundary (GB) and bulk-electrode interface/space charge polarization (SCP) have been separated with the help of this fitted data (Figure 6 (b) of main text). It is known that SCP appears at low frequencies, therefore, the first parallel combination (CPE1-R1) is representing SCP region as low frequency (500 Hz to 1 khz) data is fitted and simulated by varying the values of mainly CPE1 and R1. It appears that the large semicircular arc (10 3 Hz to 10 7 Hz) has only a single curvature but actually it consists of two curvatures and it is alone fitted with a series combination of two capacitors; each having a resistance in parallel individually (i.e.,c1-r2 and C2-R3). In this regard, a segment of this arc was fitted and simulated separately for a parallel combination of a capacitor and a resistor (C2-R3). Consequently, a new simulated smaller semicircle, corresponding to C2-R3, is observed as shown in Figure 6 (b) of main text. Since, this small segment is corresponding to higher range of probing frequency (10 6 Hz to 10 7 Hz), hence, it has been recognized as the region corresponding to grains contribution. The remaining segment corresponding to midrange of probing frequency (10 3 Hz to 10 6 Hz), fitted mainly with the variation in C1 and R2, has been assigned as the GB region. In this way, in present sample, three different capacitance regions have been identified. These were separated on the basis of corresponding (i) frequency range and (ii) value of resistance obtained after data fitting and hence recognized as SCP (CPE1- R1), GB (C1-R2) and grains (C2-R3) contributions accordingly. Now, as far as the effect of magnetic field is concern, the resistance corresponding to grain contribution is found to be almost equal in the absence (H=0T) and presence (H=0.2T to H=1.2T) of magnetic field whereas the resistance corresponding to both SCP and GB is decreasing with increasing magnetic field which is clearly distinguishable also in Figure 6 (b) of main text and following Figure S6. Since, the comparison of resistance in the absence (H=0T) and presence (H=0.2T to H=1.2T) of magnetic field is the main concern of present MRIS study, therefore, present S10

11 EIS analysis is limited only upto the identification of above mentioned regions (i.e. SCP (CPE1-R1), GB (C1-R2) and grains (C2-R3)) which are contributing to observed magneto capacitance at corresponding frequencies. FIGURE-S6: Room-temperature Cole-Cole plot recorded for La γ in the absence (H=0.0 T) and presence (H=0.2 T to 1.2 T) of magnetic field. For clarity, the data corresponding to entire range of probing frequencies is shown in the inset whereas mid-high range frequency data (enclosed by a rectangular green box in the inset) is magnified as main panel. To visualise the effect of magnetic field with more clarity, this mid-high range frequency data is further magnified and shown accordingly in Figure 6 (a) and 6 (b) of main text. TABLE S7: Charge on cation/anion calculated (by considering cation vacancy) through bond-valance-sum calculations in Fullprof suit. Vacant cation site charge on cation/anion La 1 2 Ideal case (No vacancy) Vacancies at only La (A) site Vacancies at only (B) site Vacancies at only (B) site References (1) ur, A.; Shrivastava, B. D.; Nigam, H. L. X-Ray Absorption Fine Structure (XAFS) Spectroscopy A Review. Proc. Indian Natl. Sci. Acad. 2013, 79, (2) Rai, H. M.; Saxena, S. K.; Late, R.; Mishra, V.; Rajput, P.; Sagdeo, A.; Kumar, R.; Sagdeo, P. R. bservation of Large Dielectric Permittivity and Dielectric Relaxation Phenomenon in Mn-Doped Lanthanum llate. RSC Adv. 2016, 6, (3) Sagdeo, A.; utam, K.; Sagdeo, P. R.; Singh, M. N.; Gupta, S. M.; Nigam, A. K.; Rawat, R.; Sinha, A. K.; Ghosh, H.; nguli, T.; et al. Large Dielectric Permittivity and Possible Correlation between Magnetic and Dielectric Properties in Bulk Ba 3 δ. Appl. Phys. Lett. 2014, 105, S11