**Volume 68** **Part 1** Page 91 February 2012 Received 30 October 2011 Accepted 7 November 2011 Online 6 January 2012 | ## Lattice constants and thermal expansion of H_{2}O and D_{2}O Ice I*h* between 10 and 265 K. Addendum ^{a}Institut für Kristallographie, Universität Tübingen, D-72070 Tübingen, Germany,^{b}Hasylab/ DESY, Notkestrasse 85, D-22603 Hamburg, Germany, and ^{c}GZG Abt. Kristallographie, Universität Göttingen, Goldschmidtstrasse 1, D-37077 Göttingen, Germany Correspondence e-mail: wkuhs1@gwdg.de In a previous paper we reported the lattice constants and thermal expansion of normal and deuterated ice I*h* [Röttger *et al.* (1994). *Acta Cryst.* B**50**, 644-648 ]. Synchrotron X-ray powder diffraction data were used to obtain the lattice constants and unit-cell volumes of H_{2}O and D_{2}O ice I*h* in the temperature range 15-265 K. A polynomial expression was given for the unit-cell volumes. It turns out that the coefficients quoted have an insufficient number of digits to faithfully reproduce the volume cell data. Here we provide a table with more significant digits. Moreover, we also provide the coefficients of a polynomial fit to the previously published *a* and *c* lattice constants of normal and deuterated ice I*h* for the same temperature range. |

In a previous paper we reported the lattice constants and thermal expansion of normal and deuterated ice I*h* (Röttger *et al.*, 1994). Synchrotron X-ray powder diffraction data were used to obtain the lattice constants and unit-cell volumes of H_{2}O and D_{2}O ice I*h* in the temperature range 15-265 K. A polynomial expression was given for the unit-cell volumes. It turns out that the coefficients quoted have an insufficient number of digits to faithfully reproduce the volume cell data. This is due to the large correlations amongst the terms of even as well as uneven order. Here we provide a table with more significant digits and also correct one rounding error for the *A*_{3} term of the H_{2}O unit-cell volume. Moreover, we also provide the coefficients of a polynomial fit to the previously published *a* and *c* lattice constants of normal and deuterated ice I*h* for the same temperature range. In Table 1 these coefficients are given together with the quality of the fit. The database is identical to that given in Röttger *et al.* (1994). The coefficients *A*_{1} and *A*_{2} were set to zero as the thermal expansivity and its temperature derivative are assumed to be 0 at *T* = 0 K. Under this assumption the validity of the polynomial expressions is from 0 to 265 K. Finally, we like to recall that a many-term polynomial expression was adopted to faithfully represent the measured data and not because there is a particular meaning in the various higher-order terms. We indicate that other approaches could be chosen based on various empirical quasi-harmonic approximations (Reeber & Wang, 1996; Wang & Reeber, 1995) with a different set of parameters; the validity of these approximations for the ice I*h* case remains, however, to be proven and will not be attempted here. In concluding we note that the marked isotopic difference of lattice constants between deuterated and normal ice I*h* so clearly established by our data is still far from being understood (Herrero & Ramírez, 2011).

| Unit-cell volume H_{2}O ice I*h* | Lattice constant **a** H_{2}O ice I*h* | Lattice constant **c** H_{2}O ice I*h* | Unit cell volume D_{2}O ice I*h* | Lattice constant **a** D_{2}O ice I*h* | Lattice constant **c** D_{2}O ice I*h* | *A*_{0} | 128.2147 (159) | 4.4969_{15} (2) | 7.3211_{25} (3) | 128.3316 (151) | 4.4982_{8} (2) | 7.3233_{6} (6) | *A*_{1} = *A*_{2} | 0 | 0 | 0 | 0 | 0 | 0 | *A*_{3} | -1.3152 (2643) × 10^{-6} | -1.9790 (3205) × 10^{-8} | -2.4944 (6146) × 10^{-8} | -2.2616 (6547) × 10^{-6} | -3.9099 (7361) × 10^{-8} | -3.0567 (1.4264) × 10^{-8} | *A*_{4} | 2.4837 (5228) × 10^{-8} | 3.8958 (6356) × 10^{-10} | 4.6735 (1.2806) × 10^{-10} | 5.1581 (1.7731) × 10^{-8} | 9.7883 (2.1911) × 10^{-10} | 5.9033 (2.9651) × 10^{-10} | *A*_{5} | -1.6064 (3876) × 10^{-10} | -2.6930 (4820) × 10^{-12} | -2.9799 (9966) × 10^{-12} | -4.5811 (1.9116) × 10^{-10} | -9.7393 (2.5879) × 10^{-12} | -3.9203 (2.3100) × 10^{-12} | *A*_{6} | 4.6097 (1.2625) × 10^{-13} | 8.2861 (1.6256) × 10^{-15} | 8.3902 (3.4003) × 10^{-15} | 2.0890 (1.0144) × 10^{-12} | 4.9329 (1.4896) × 10^{-14} | 1.1541 (7936) × 10^{-14} | *A*_{7} | -4.9661 (1.5196) × 10^{-16} | -9.5759 (2.0415) × 10^{-18} | -8.8400 (4.2799) × 10^{-18} | -4.8591 (2.6388) × 10^{-15} | -1.2573 (4168) × 10^{-16} | -1.2751 (1.0119) × 10^{-17} | *A*_{8} | 0 | 0 | 0 | 4.5747 (2.6900) × 10^{-1} | 1.2798 (4546) × 10^{-19} | 0 | ^{2} | 6.91 | 8.84 | 9.36 | 6.12 | 10.28 | 3.97 | | |

Herrero, C. P. & Ramírez, R. (2011). *J. Chem. Phys.* **134**, 094510.

Reeber, R. R. & Wang, K. (1996). *Mater. Chem. Phys.* **46**, 259-264.

Röttger, K., Endriss, A., Ihringer, J., Doyle, S. & Kuhs, W. F. (1994). *Acta Cryst.* B**50**, 644-648.

Wang, K. & Reeber, R. R. (1995). *J. Appl. Cryst.* **28**, 306-313.