Nat

ion

al S

cien

ce F

ou

nd

atio

nN

atio

nal

Sci

ence

Fo

un

dat

ion Atomic Defects Hop to the Tune of Music

Outcome: Researchers led by Texas A&M University materials scientist Miladin Radovic showed that large amplitude vibrations at the resonant frequencies can be

Miladin Radovic, Texas Engineering Experiment Station, DMR 1057155

Effects of Anelastic Relaxation of Defect Complexes on the Mechanical Behavior of Oxide

Impact: Besides damping catastrophic resonant vibrations at high temperatures, this discovery could pave the way for new high temperature sensors and more reliable electro chemical energy conversion devices, such as fuel cells. These materials may also help dissipate sonic and ultrasonic vibrations in the large temperature range.

Prof. Radovic and Ph.D. student Peipei Gao next to the high temperature resonant ultrasound spectrometer developed at Texas A&M University. (courtesy Texas A&M University)

significantly attenuated or damped in some metal-oxide ceramics even at elevated temperatures due to reorientation of the clusters of the atomic defects

Explanation: All objects oscillate at a greater amplitude at specific frequencies known as resonant frequencies. At these frequencies, even small periodic driving force can produce large amplitude vibrations, violent swaying motions and even catastrophic failure. One familiar example is the wine glass which can shatter when exposed to the sound. .

Nat

ion

al S

cien

ce F

ou

nd

atio

nN

atio

nal

Sci

ence

Fo

un

dat

ion

Professor Miladin Radovic from Texas A&M University and recipient of an NSF Faculty Early Career Development (CAREER) award, led the team, which showed that large amplitude vibrations at the resonant frequencies can be significantly attenuated or damped in some, essentially rigid and brittle, metal-oxide ceramics even at elevated temperatures due to reorientation of the clusters of the atomicdefects (dopant-oxygen vacancy) that are common in those ceramics. In most of the technologically important metal oxides, a part of the host metal ions are substituted by another metal ions to tailor their physical properties. This so called doping frequently results in the formation of the oxygen vacant sites in the crystal structure that is adjacent to the substitute metal ions. When these doped oxides are exposed to the small periodic driving forces such as sound or ultrasound vibrations, oxygen ions jump in and from those vacant sites. Their hopping with the mechanical vibrations or waves dissipates a large portion of mechanical energy and attenuate resonance amplitude. The characteristic temperature and resonant frequency with the maximum attenuation

0 100 200 300 400 500 600 700 8000.00E+00

2.00E-03

4.00E-03

6.00E-03

8.00E-03

1.00E-02

AluminaCEO10GDC20GDC20SDC20LDC

Temperature (ºC)

Att

enu

atio

n (

Q-1

)

0.010

0.008

0.006

0.004

0.002

0.000

Attenuation (or damping coefficient), Q-1, vs. temperature determined by RUS for pure alumina ,cerium-oxide, CEO, and cerium-oxides doped with gadolinium-oxide, 10GDC and 20GDC, samarium-oxide, 20SDC, and lanthanum-oxide, 20LDC.(courtesy Texas A&M University)

Miladin Radovic, Texas Engineering Experiment Station, DMR 1057155

Nat

ion

al S

cien

ce F

ou

nd

atio

nN

atio

nal

Sci

ence

Fo

un

dat

ion

was found to depend on the size of the substitute metal ion relative to the size of the host metal ion and amount of substituted metal ions. Therefore, this finding can be used to tailor mechanical response of oxide ceramics that are widely used in sensors and energy conversion devices by their selective doping with other oxides.

An integrated education and outreach effort of this project includes providing undergraduate and graduate students with hands-on training and incorporating the latest research results into new materials science and renewable energy courses. The high temperature Resonant Ultrasound Spectrometer, RUS, been developed and sequentially improved over years by undergraduate students: Patrick Mahaffey and Mathew Westwick. It has been used as demonstration tool in the class room.

Miladin Radovic, Texas Engineering Experiment Station, DMR 1057155