@conference{
author = "Dapčević, Aleksandra and Luković Golić, Danijela and Radojković, Aleksandar and Ćirković, Jovana and Branković, Goran and Branković, Zorica",
year = "2016",
abstract = "The magnetoelectric multiferroics are one of the most promising materials in recent years
due to their possible application in data storage, sensors, and spintronic devices. Bismuth
ferrite, BiFeO3, is a well-known multiferroic material which exhibits the coexistence of
ferroelectricity and magnetism well above room temperature. The magnetic, electrical and
optical properties of BiFeO3 can be improved by doping with lanthanoides, since these
dopants induce larger magnetization [1].
Gadolinium doped microcrystalline samples of BiFeO3 were synthesized from
Bi(NO3)3·5H2O, Gd(NO3)3·6H2O and Fe(NO3)3·9H2O, by hydro-evaporation procedure
presented by Sakar et al. [2]. Previously dissolved starting components were mixed and
heated at 80 °C under magnetic stirring until complete evaporation. The brown-red precursor powders obtained after drying for 2 h at 90 °C were calcined at 650 °C in a tube
oven for 3 h to form resulting Bi1–xGdxFeO3 (x = 0.075, 0.05, 0.03 and 0.01) powders.
Afterwards, the powders were pressed into pellets and sintered for 6 h at 870 °C.
The XRD data of pulverized sintered samples were collected using an Ital Structure
APD 2000 X-ray powder diffractometer (CuKα radiation, λ = 1.5418 Å) in a
range 20 – 100 °2θ with a step-width of 0.02 ° and a constant counting time of 10 s per
step. The FULLPROF software was used for the Rietveld refinement of the structure in
WINPLOTR environment.
The XRD powder patterns revealed that the dominant phase was rhombohedral
Bi1-xGdxFeO3 (space group R3c). A small amount (less than 3 %) of Bi2Fe4O9 phase was
found in each sample. The trend of decreasing unit-cell volumes with the increase of Gdcontent has been observed.
The positions of all atoms, (Bi,Gd)–Fe distances and Bi–O bond lengths are calculated
in order to verify the cation displacement along [111], which is a good indicator of electrical polarization of Bi1-xGdxFeO3 samples. The greatest lattice distortion was found for
the sample with the highest Gd-content, i.e. Bi0.925Gd0.075FeO3, and therefore the largest
electric polarization is expected here. The highest antiferromagnetic ordering at room temperature can be expected for the sample with the lowest Gd-content, i.e. Bi0.99Gd0.01FeO3,
since it has the smallest Fe–O–Fe bond angle. This angle indicates the extent of Fe(3d)–
O(2p) orbital overlapping in the crystal structure, which is responsible for the antiferromagnetic coupling between next-nearest-neighbor Fe3+ cations via O2-
anion.
[1] A. Mukherjee, S. Basu. P. K. Manna, S. M. Yusuf, M. Pal, J. Mater. Chem., C2 (2014)
5885–5891.
[2] M. Sakar, S. Balakumar, P. Saravanan, S. N. Jaisankar, Mater. Res. Bull., 48 (2013)
2878–2885., Magnetno-električni multiferoici jedni su od najatraktivnijih materijala
poslednjih godina s obzirom na moguću primenu u uređajima za skladištenje podataka,
senzorima i ,,spintronic” uređajima. Bizmut-ferit, BiFeO3, je poznati multiferoik za koga
je karakteristično postojanje i feroelektriciteta i magnetizma iznad sobne temperature.
Magnetna, električna i optička svojstva BiFeO3 mogu se poboljšati dopiranjem lantanoidima jer ovi dopanti povećavaju magnetizaciju [1].
Mikrokristalni uzorci gadolinijumom dopiranih BiFeO3 dobijeni su metodom potpunog otparavanja rastvarača, tj. vode, prema proceduri koju su predložili Sakar i koautori
[2]. Mešanjem na magnetnoj mešalici rastvora Bi(NO3)3·5H2O, Gd(NO3)3·6H2O i
Fe(NO3)3·9H2O i njihovim zagrevanjem do 80 °C i potpunog uparavanja, nastali su
prahovi mrkocrvene boje. Nakon sušenja tokom 2 h na 90 °C, prahovi su kalcinisani na
650 °C u cevnoj peći tokom 3 h. Dobijeni mikrokristalni uzorci sastava Bi1–xGdxFeO3
(x = 0,075, 0,05, 0,03 i 0,01) ispresovani su u vidu tableta i sinterovani 6 h na 870 °C.
Podaci za Ritveldovo utačnjavanje prikupljeni su na sprašenim sinterovanim uzorcima
na difraktometru Ital Structure APD 2000 sa CuKα zračenjem (λ = 1,5418 Å) u intervalu 20 – 100 °2θ sa korakom od 0,02 ° i vremenom zadržavanja od 10 s po koraku. Za
utačnjavanje strukture korišćeni su programski paketi FULLPROF i WINPLOTR.
Analizom difraktograma najpre je određen fazni sastav polikristalnih uzoraka. U svim
uzorcima identifikovan je romboedarski Bi1-xGdxFeO3 (prostorna grupa R3c) uz prisustvo
manje od 3 % faze Bi2Fe4O9. Primećen je trend smanjenja zapremine jedinične ćelije sa
povećanjem sadržaja gadolinijuma.
Nakon što su određeni položaji atoma, izračunate su vrednosti rastojanja (Bi,Gd)–Fe i
dužine veza Bi–O da bi se procenilo izmeštanje katjona duž [111], jer je ono dobar pokazatelj električne polarizacije u uzorcima Bi1-xGdxFeO3. Najveća električna polarizacija
predviđa se za uzorak sa najvećim sadržajem dopanta, tj. Bi0,925Gd0,075FeO3, s obzirom na
to da je najveće rastojanje između katjona nađeno kod ovog uzorka. Očekuje se da uzorak
sa najnižim sadržajem dopanta, tj. Bi0,99Gd0,01FeO3, ima najizraženiji antiferomagnetizam
jer ga karakteriše najmanji ugao Fe–O–Fe. Ovaj ugao pokazuje nivo preklapanja Fe(3d)–
O(2p) orbitala u kristalnoj strukturi, od koga zavisi antiferomagnetno sprezanje između
nesusednih Fe3+
-katjona preko O2–
-anjona.",
publisher = "Srpsko kristalografsko društvo, Srbija",
journal = "XXIII Conference of the Serbian Crystallographic Society",
title = "GADOLINIUM DOPED BISMUTH FERRITE",
pages = "67-66",
url = "https://hdl.handle.net/21.15107/rcub_rimsi_2742"
}
