Bismuth Ferrite

The potential of future electronic memory devices are at its

twilight of booming into a new set of generation of memory chips.

Instead of having the memory devices of which are as big as tens

of nanometer, which is what our today technology’s advanced

system offers, comes a memory device shrinking to one or two

nanometer. If only one can synthesize a way to gasp into his

hands the controls of how to separate those regions that have

different electric, magnetic and other properties this would be

possible.

Bismuth ferrite is a compound of bismuth, iron and oxygen—

BiFeO3. This compound was discovered to have domain walls never

been seen by scientists of the department of energy at Lawrence

Berkeley National Laboratory of the University of California.

Even though Bismuth ferrite was originally know as an insulator,

this compound was discovered to have different electrical

polarity that conducts electricity at room temperature. In this

review, I will focus primarily on the synthesis, physical and

chemical properties, industry use and its effect upon disposal to

the environment of Bismuth Ferrite.

Chemical and physical properties

Bismuth ferrite, being an inorganic chemical compound, has

perovskite structure ( in which planes of heavy atoms, bismuth

for this compound, and oxygen alternates with planes of lighter

atoms, Iron for this compound, and oxygen atoms) and is said to

be one of the most promising multiferroic materials that exhibits

multiferroic properties at room temperature. At room temperature,

BiFeO3 is classified as rhombohedral that belongs to group R3c.

It is synthesize in thin film and in bulk and it temperatures—

antiferrmagnetic Neel and ferroelectric Curie—are well above room

temperature (653 K nd 1100 K, respectively). Its polarization

occurs with a magnitude of 90-95 µC/cm2 along the pseudocubic 111

direction. Its walls are oriented along two different

crystallographic planes, meaning it can be separated with 109-

degree, 71-degree, or 180-degree differences in the direction of

the polarization. Bismuth ferrite films contains ferroelectric

sphere that is between 5 to 10 micrometers. It exhibits week

magnetism at room temperature because of the spiral magnetic spin

cycloid with a periodicity of 62 nm.

Synthesis/preparation of Bismuth ferrite

In synthesizing this promising alloy, many ways were

developed. The following are just some of the ways on how to

produce Bismuth ferrite:

SOL-GEL TECHNIQUE

A 2:1 ratio of bismuth and iron was prepared from the

starting materials bismuth nitrate and ferric chloride. The

excess bismuth is used to compensate the bismuth evaporated

during high temperature annealing. Bismuth nitrate and ferric

chloride were dissolved in acetic acid and was added with

ethylene glycol that served as a drying control agent to restrict

cracking of the thin films before coat spinning. The solution was

them refluxed for 5 hour.

Figure 1. Flow chart of the

synthesis of BiFeO3 .

The precursor was coated on

copper substrate at 3000 rpm for 30

seconds while spinning after it was

cooled down to room temperature.

For thicker film, the process was

repeated. After the process, the film

was kept exposed for 1 hour for gel film to form via hydrolysis

Figure 1

and polymerization. The film was dried via heat treatment at a

temperature of 300o C for 2 hours. The Crystallization,

densification and microstructure of the films were then examined.

SUPERFACTANT ASSISTED AUTOCOMBUSTION SYNTHESIS

Bismuth ferrite powder was

synthesized by a solution

evaporation route. A 0.25 M Bi(NO3)3

and a 0.25 M Fe(NO3)3 was prepared by

dissolving it in dilute nitric acid.

The two solutions were mixed in a

beaker. A 0.1 mole ratio of glycine

was added to the solution above with

respect to nitrate. The supernatants

Triton X, and ALS (ammonium lauryl

sulfate) were added to the solution

with a mole ratio of 0.05

with respect to the metals. The solution was then heated on a hot

plate with continuous stirring until it reaches its boiling

temperature such time that all liquid have already evaporated. A

brown fume that evolves during the process was obtained at the

bottom of the beaker. The powder was than calcined at 500oC and

550oC. the crystalline size of the powder was then computed using

the Scherrer formula.

Figure 2

Figure 2. Flow chart of supernatant assisted autocombustion

synthesis.

SUPER CRITICAL HYDROTHERMAL SYNTHESIS

The equal mole amount (0.003 mol) of Bi(NO3)3·5H2O and

Fe(NO3)3.9H2O was weighted. Then, Bi(NO3)3.5H2O and Fe(NO3)3.9H2O

was dissolved in 250 ml deionized water and was heated until

homogenized. It was than transferred to a reactor vessel. A

stainless steel 316 with 180 mL volume bath type reactor was used

and was heated using an electrical heater.

The hydrothermal reaction was performed in the reactor

vessel at 500o C for 2 hours. After then, the reactor vessel was

reduced to stop the reaction with cold water so that the product

will be collected through washing the reactor with deionized

water and cetrifugate to remove the reagent that didn’t reacted.

Then the BiFeO nanoparticles were dreid at 40o C for 24 hours.

The identity of the synthesized nanoparticled was then X-

rayed for diffraction measurements. The size and the shape of the

obtained nanoparticled was then studied using transmission

electron microscopy.

Important use in the industry

In the past studies, bismuth ferrite has proven itself for

its effective and applications to the industry. Bismuth ferrite

was used as high tech magnetic tapes, used for its

superconductivity, used in environmental engineering; and

finally, is used to enhance spontaneous magnetization. But for

this review, I will focus on the new discovered application of

bismuth ferrite--nanoscale shape-memory oxide.

Bismuth ferrite is a compound of bismuth, iron and oxygen.

This multiferroic compound has been studied thoroughly in recent

years by many scientists. As bismuth ferrite, being a

multiferroic alloy, displays both ferromagnetic and ferroelectric

properties, meaning it responds to applications of magnetic field

or external electric. In this latest study by the scientists of

the University of California in Berkley they were able to

introduce an elastic-like phase transition into bismuth ferrite

by means of electric field.

Bismuth ferrite's application to the electric field allowed

them to develop a phase transformation to be achieve that is

reversible even without assistance of an external stress recovery

said Ramesh of the University of California in Berkley.

This new discovery of the shape-memory alloys claimed to be

the champion for elasticity and is primed to take over the shape

memory apps to a whole new level---which is shrinking it to

nanoscale. Researchers in Berkley laboratory have discovered a

way to introduce recoverable strain into bismuth ferrite up to

14%.

This is larger than any shape-memory effect observed in any

metals for now. This discovery opens new door to for the

application of many fields such as that in medical, energy, and

specially electronics.

According to Jinxing Zhang this bismuth ferrite they newly

developed displays amazing features including being stable even

when reduced to nanometer compared to other shape-memory alloys.

One more feature is that its responses are fast due the

electrical field needed to activate shape-memory alloy rather

than the primitive way of using thermal fields.

A shape-memory effect is when a solid material grows back to

its original shape after being deformed after stress is applied

is an ability of a metal to be elastic. In the past, this has

always been involved with heating. Nickel-titanium or "nitinol”

alloy is a shape-memory alloy that has a great use to those that

are in the field of medicine. It is used intents for angioplasty

and in medical joints. This memory effect of alloy has also have

a great impact for non-medical fields. An example is the

actuators in smart materials and in Microelectro-Mechanical

Systems (MEMS). But as scientist try to achieve nano-scale size

of this shape-memory alloys, various problems and instabilities

arises such as micro-cracking and oxidation. But with the new

study on bismuth ferrite, scientists of Berkley Lab's materials

Sciences Division of the University of California in Berkley were

able to eliminate surface issues and were able to integrate it

with microelectronics by achieving shape-memory effect to an

oxide material rather than in alloy metals. According to Zhang,

this bismuth ferrite they developed has "ultra-high work function

density during actuation that is almost two orders of magnitude

higher than what a metal alloy can generate." Ramesh also added

that even though aspects like hysteresis, micro-cracking and so

many more needs to be accounted when it will be applied to real

devices, the discovery of bismuth ferrite being able to show

large shape-memory effect only shows that it is not an ordinary

material. This alloy has great potentials that it can be use in

the future in nanoelectromechanical devices and other state-of-

the-art nanosystems.

References:

Researchers Discover Nanoscale Shape-memory Oxide. (n.d.). In PCB

Design 007. Retrieved December 20, 2013, from

http://www.pcbdesign007.com/pages/zone.cgi?

a=96945&artpg=1&topic=0

Physicists observe new magnetic state of bismuth ferrite (n.d.).

In Phys.org. Retrieved December 20, 2013, from

http://phys.org/news/2013-05-physicists-magnetic-state-bismuth-

ferrite.html#inlRlv

Remembrances of Things Past: Berkeley Lab Researchers Discover

Nanoscale Shape-Memory Oxide (n.d.). In Hispanicbusiness.

Retrieved December 20, 2013, from

http://www.hispanicbusiness.com/2013/12/3/remembrances_of_things_

past_berkeley_lab.htm

Researchers take the lead out of piezoelectrics (n.d.). In

Phys.org. Retrieved December 20, 2013, from

http://phys.org/news177340310.html

Hu, Y., Fei, L., Zhang, Y., Yuan, J., Wang, Y., and Gu, H.,

(2010). Synthesis of Bismuth Ferrite Nanoparticles via a Wet

Chemical Route at Low Temperature. Hindawi Publishing

Incorporated, 2011(2011), 6 pages. Retrieved from

http://www.hindawi.com/journals/jnm/2011/797639/

Haneberg, D. H. (2011). A Finite-Size Study on Samarium-

Substituted Bismuth Ferrite: Multiferroic and Lead-Free

Piezoelectric Materials. Abstract retrieved from NTNU.

Shurygina V.Yu., Zhereb V.P., Skorikov V.M. (2013). MECHANISM OF

SOLID STATE SYNTHESIS OF BISMUTH FERRITE BI25FEO39. Abstract from

Digital scientific journal

PDF:

Bismuth ferrite nanoparticles formation via a supercritical

hydrothermal synthesis method (2012) by J. Karimi, A., and

Golzary, C

Synthesis and Properties of Bismuth Ferrite Multiferroic

Nanoflowers (2000’s) by Chybczynska, K., Ławniczak, P., Hilczer,

B., Łeska, B., Pankiewicz, R., Pietraszko, A., Kepinski, L.,

Kałuski, T., Cieluch, P., Matelski F., and Andrzejewski, B.