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Copyright: American Scientific Publishers
RESEARCH ARTICLE
Copyright © 2012 American Scientific Publishers
All rights reserved
Printed in the United States of America
Journal of
Computational and Theoretical Nanoscience
Vol. 9, 1541–1545, 2012
Effect of Nucleators and Intermediates on the
Magnetic Properties of Nanosized Magnetite
Obtained by Glass Crystallization
Viorel Sandu
1 ∗
, Mirela Sidonia Nicolescu
1
, Victor Kuncser
1
, Stelian Popa
1
,
Iuliana Pasuk
1
, and Elena Sandu
2
1
National Institute of Materials Physic-Bucharest, 105b Atomistilor Street, Magurele, 077125, Romania
2
Horia Hulubei National Institute of Physics and Nuclear Engineering, 407 Atomistilor Street, Magurele, 077125, Romania
We investigate the role of chromium and phosphorous oxides on the growth and magnetic properties
of crystallized Fe-containing borosilicate glasses as well as their evolution under different thermal
processing. The glasses have the ratio between SiO
2
and Fe
2
O
3
in the range 1.49 to 2.68 and
Al
2
O
3
/MgO as intermediate/modifier oxides. X-ray diffraction and Mössbauer spectroscopy data
revealed the presence of magnetite as the major crystalline phase in all as-prepared samples
but additional amounts of hematite and of Fe-rich paramagnetic phases are also visible in some
samples. The magnetic response is correlated with the disorder observed in the different sites
(tetrahedral and octahedral) of the magnetite.
Keywords: Magnetite, Glass Crystallization, Mössbauer Spectroscopy, Verwey Transition,
Magnetization.
1. INTRODUCTION
Single phase crystallization from a polynar glass melt is
always a challenge. The choice of composition, including
intermediates, modifiers, and nucleators is very important
in developing a dispersed nanograined crystalline phase
in a vitreous matrix. The crystalline grains could nucle-
ate and growth either during the cooling down of the
molten composition or as a result of different procedures
of heat treatments. The growth of single phase magnetic
nanoparticles within a vitreous matrix is of special inter-
est. They can provide silica dressed single or multido-
main nanoparticles for different applications.
1
Among all,
ferrimagnetic iron oxide or magnetite (Fe
3
O
4
) are very
appreciated for medical applications due to its compati-
bility with living cells. However, iron containing glasses
can develop several types of iron compounds depending
on chemical composition, and process parameters. More-
over, even when magnetite crystallizes as a major phase,
its structure, hence, the magnetic response, is significantly
influenced by those parameters.
2–6
Magnetite has an inverse spinel cubic structure where
the tetrahedral sites A are occupied with Fe
3+
A
ions whereas
the octahedral sites B are equally shared by Fe
3+
B
and
Fe
2+
B
ions. Below 851 K, the magnetic moments at A sites
∗
Author to whom correspondence should be addressed.
are aligned antiparallely to the magnetic moments at
B sites, resulting in a ferrimagnetic state. Consequently,
the formation of magnetite requires a minute equilibrium
between Fe
2+
and Fe
3+
ions. In a glass melt, both ions
coexist and, in a oxidizing atmosphere, react with the
physically dissolved oxygen following the redox reaction:
4Fe
3+
+ 2O ⇆ 4Fe
2+
+ O
2
. Fe
3+
enters tetrahedral coor-
dination (FeO
4
wheras, Fe
2+
enters octahedral coordina-
tion, (FeO
6
, hence, the ratio of two ions depends strongly
on the composition of the melt. For exemple, Fe
3+
in
tetrahedral position which means FeO
4
competes the triva-
lent modifiers present in the glass melt (like Al
3+
for
the charge compensation from a monovalent ion (Na)
while Fe
2+
competes with bivalent modifiers (e.g., Mg
2+
.
Therefore, the crystallization of magnetite as unique phase
requires a careful choice of both glass modifiers and
nucleators as well as of the heat treatments.
In our contribution we analyze the role of Cr
2
O
3
and
P
2
O
5
as nucleators in conjunction with Al
2
O
3
and MgO
2
as intermediates and modifiers in the growth of magnetite
as major phase from a borosilicate glass melt.
2. SAMPLE FABRICATION
A series of five ferrimagnetic glass-ceramic samples were
obtained by crystallization from iron containing borosil-
icatic glass melts with oxide compositions shown in the
J. Comput. Theor. Nanosci. 2012, Vol. 9, No. 9 1546-1955/2012/9/1541/005 doi:10.1166/jctn.2012.2241 1541