New technique controls crystalline structure of titanium dioxide

Jun 27, 2012
A new technique allows researchers to control the phase of the titanium dioxide by modifying the structure of the titanium trioxide and sapphire substrate. Credit: Dr. Jay Narayan, North Carolina State University

Researchers from North Carolina State University have developed a new technique for controlling the crystalline structure of titanium dioxide at room temperature. The development should make titanium dioxide more efficient in a range of applications, including photovoltaic cells, hydrogen production, antimicrobial coatings, smart sensors and optical communication technologies.

Titanium dioxide most commonly comes in one on of two major "phases," meaning that its atoms arrange themselves in one of two crystalline structures. These phases are "anatase" or "rutile." The arrangement of atoms dictates the material's optical, chemical and . As a result, each phase has different characteristics. The anatase phase has characteristics that make it better suited for use as an and for applications such as . The rutile phase is better suited for use in other applications, such as , and technologies.

"Traditionally, it has been a challenge to stabilize titanium dioxide in the desired phase," says Dr. Jay Narayan, John C. Fan Distinguished Chair Professor of Materials Science and Engineering at NC State and co-author of a paper describing the work. "The material tends to transform into the anatase phase below 500 degrees Celsius [C], and transform into the rutile phase at temperatures above 500 C.

"We have now developed a technique that precisely controls the phase, or , of titanium dioxide at room temperature – and stabilizes that phase, so it won't change when the temperature fluctuates. This process, called phase tuning, allows us to fine-tune the structure of the titanium dioxide, so that it has the optimal structure for a desired application."

The process begins by using a widely available sapphire substrate that has the desired crystalline structure. Researchers then grow a template layer of titanium trioxide on the substrate. The structure of the titanium trioxide mimics the structure of the sapphire substrate. The titanium dioxide is then grown on top of the titanium trioxide template layer.

The structure of the titanium dioxide differs from the titanium trioxide – but is dictated by the structure of that template layer. This means that you can create the in any phase, simply by modifying the structure of the titanium trioxide and sapphire substrate.

This works because of a process called domain matching epitaxy (DME). In DME, the lattice planes in the template layer line up with the lattice planes of the material being grown on that template. Lattice planes are the lines, or walls, which constitute a crystal.

The paper, "Domain epitaxy in TiO2/[alpha]-Al2O3 thin film heterostructures with Ti2O3 transient layer," is published online June 20 in Applied Physics Letters. The paper was co-authored by M.R. Bayati and R. Molaei, Ph.D. students at NC State; Dr. Roger Narayan, a professor in the joint biomedical engineering department of NC State and the University of North Carolina at Chapel Hill; Dr. H. Zhou, a postdoctoral researcher at NC State; and Dr. S.J. Pennycook of Oak Ridge National Laboratory. The research was funded by the National Science Foundation.

The researchers have also demonstrated how this technique can be used with silicon computer chip substrates, which can be integrated into electronics such as smart sensors.

Explore further: Researchers develop scalable methods for manufacturing metamaterials

Related Stories

Graphene boosts efficiency of next-gen solar cells

Apr 24, 2012

(Phys.org) -- The coolest new nanomaterial of the 21st century could boost the efficiency of the next generation of solar panels, a team of Michigan Technological University materials scientists has discovered.

Toward a more efficient use of solar energy

Apr 14, 2011

The exploitation and utilization of new energy sources are considered to be among today's major challenges. Solar energy plays a central role, and its direct conversion into chemical energy, for example hydrogen generation ...

Recommended for you

Novel technique opens door to better solar cells

Apr 14, 2014

A team of scientists, led by Assistant Professor Andrivo Rusydi from the Department of Physics at the National University of Singapore's (NUS) Faculty of Science, has successfully developed a technique to ...

User comments : 1

Adjust slider to filter visible comments by rank

Display comments: newest first

Macksb
1 / 5 (1) Jun 28, 2012
Rutile is the most common form. Name comes from Latin word for red, rutilus. Some specimens have a deep red color. The crystal structure is a primitive tetragonal unit cell.

Anatase comes from the Greek word for extension, anatasis. It also crystallizes in a tetragonal system, but in a steeper or more extended pyramid. 82 degrees for anatase and 56 degrees for rutile, approx.

A third form, brookite, is orthorhombic.

Rutile has the lowest molecular volume, and so it's the likely outcome in higher pressure formative environments.

More news stories

Could 'Jedi Putter' be the force golfers need?

Putting is arguably the most important skill in golf; in fact, it's been described as a game within a game. Now a team of Rice engineering students has devised a training putter that offers golfers audio, ...

Health care site flagged in Heartbleed review

People with accounts on the enrollment website for President Barack Obama's signature health care law are being told to change their passwords following an administration-wide review of the government's vulnerability to the ...

Airbnb rental site raises $450 mn

Online lodging listings website Airbnb inked a $450 million funding deal with investors led by TPG, a source close to the matter said Friday.