BUFFALO, N.Y. -- New materials science research from the
University at Buffalo could hasten the creation of "smart" windows
that reflect heat from the sun on hot summer days but let in the
heat in colder weather.
The findings concern a unique class of synthetic chemical
compounds that are transparent to infrared light at lower
temperatures, but undergo a phase transition to begin reflecting
infrared when they heat up past a certain point.
An article detailing some of these discoveries appears today
(April 7) on the cover of the Journal of Physical Chemistry
Letters. Additional papers have appeared online or in print in
CrystEngComm, the Journal of Materials Chemistry and Physical
Review B. The research is described in a video at http://pubs.acs.org/page/jpclcd/banerjee-video.html
In the papers, UB researchers report that they have managed to
manipulate the trigger temperature for vanadium oxide, one such
material. The advance is a crucial step toward making the compound
useful for applications such as coatings for energy-saving
By preparing vanadium oxide as a nanomaterial instead of in
bulk, the scientists managed to lower the compound's trigger point
from 153 degrees Fahrenheit to 90. Doping vanadium oxide nanowires
with tungsten brought the temperature down further, to 7 degrees
Fahrenheit. Molybdenum doping had a similar but smaller effect.
Researchers also found that they were able to induce a phase
transition using an electric current instead of heat.
UB chemist Sarbajit Banerjee led the studies, collaborating with
Sambandamurthy Ganapathy, an assistant professor of physics, to
head the Physical Review B research on the use of the electric
"Definitely, we are closer than we've ever been to being able to
incorporate these materials into window coatings and other systems
that sense infrared light," said Banerjee, an assistant professor.
"What we found is an example of how much of a difference finite
size can make. You have a material like vanadium oxide, where the
phase transition temperature is too high for it to be useful, and
you produce it as a nanomaterial and you can then use it right
Banerjee and Ganapathy previously led research projects
demonstrating that, in nanoscale form, two additional synthetic
compounds -- copper vanadate and potassium vanadate -- exhibit
phase transitions akin to those in vanadium oxide.
Banerjee's work has caught the attention of the National
Renewable Energy Laboratory, which has contacted him to discuss
developing window coatings that could improve the energy efficiency
of buildings with heating or air conditioning systems. The
technology could be particularly useful in places like Phoenix and
Las Vegas that experience extreme summer temperatures.
Besides smart windows, vanadium oxide could also be useful in
products including computer chips, night-vision instruments and
missile guidance systems, Banerjee said.
Two major awards are funding Banerjee's research on the
material: A Cottrell Scholar Award from the Research Corporation
for Science Advancement, announced this year, and a National
Science Foundation CAREER award, the foundation's most prestigious
award for junior investigators.
Both honors recognize Banerjee's accomplishments in teaching as
well as in research. He has mentored numerous graduate students,
including Luisa Whittaker, Christopher J. Patridge and Jesus M.
Velazquez, who appear as first authors on some of Banerjee's papers
on vanadium oxide. Tai-lung Wu, supervised by Ganapathy, is the
first author of the Physical Review B paper.
The University at Buffalo is a premier research-intensive public
university, a flagship institution in the State University of New
York system and its largest and most comprehensive campus. UB's
more than 28,000 students pursue their academic interests through
more than 300 undergraduate, graduate and professional degree
programs. Founded in 1846, the University at Buffalo is a member of
the Association of American Universities.