Thermal expansion of anatase and rutile between 300 and 575 K using synchrotron powder X-ray diffraction

High-precision unit-cell parameters for the TiO2 polymorphs anatase and rutile at temperatures between 300 and 575 K have been determined using Rietveld analysis of synchrotron powder XRD data. Polynomial models were used to express the tetragonal unit-cell parameters as a function of absolute temperature, with a (anatase)=1.759 37 x 10(-8) x T-2+6.418 16 x 10(-6) x T+3.779 84, c (anatase)=6.6545 x 10(-8) x T-2+4.0464 x 10(-5) x T+9.4910, V (anatase)=2.237 58 x 10(-6) x T-2 + 1.027 77 x 10(-3) x T+ 135.602, a (rutile)=-6.636 42 x 10(-11) x T-3+ 1.005 01 x 10(-7) x T-2-1.009 93 x 10(-5) x T+4.586 34, c (rutile)=-4.115 50 x 10(-1)1 x T-3+6.405 94 x 10(-8) x T-2+4.675 61 x 10(-7)T +2.95181, and V (rutile)=-2.7790 x 10(-9) x T-3+4.2386 x 10(-6) x T-2-3.3551 x 10(-4) x T+62.100. The polynomial expressions were used to calculate linear (alpha) and volume (beta) thermal expansion coefficients of anatase and rutile between 300 and 575 K. At 298.15 K, these values were alpha(a) =4.46943 x 10(-6) K-1, alpha(c)=8.4283 x 10(-6) K-1, and beta=17.3542 x 10(-6) K-1 for anatase, and alpha(a) =6.99953 x 10(-6) K-1, alpha(c)=9.36625 x 10(-6) K-1, and beta=28.680 x 10(-6) K-1 for rutile. (C) 2007 International Centre for Diffraction Data.