addenda and errata
Lattice constants and _{2}O and D_{2}O Ice Ih between 10 and 265 K. Addendum
of H^{a}Institut für Kristallographie, Universität Tübingen, D72070 Tübingen, Germany, ^{b}Hasylab/ DESY, Notkestrasse 85, D22603 Hamburg, Germany, and ^{c}GZG Abt. Kristallographie, Universität Göttingen, Goldschmidtstrasse 1, D37077 Göttingen, Germany
^{*}Correspondence email: wkuhs1@gwdg.de
In a previous paper we reported the lattice constants and h [Röttger et al. (1994). Acta Cryst. B50, 644–648 ]. Synchrotron Xray powder diffraction data were used to obtain the lattice constants and unitcell volumes of H_{2}O and D_{2}O ice Ih in the temperature range 15–265 K. A polynomial expression was given for the unitcell 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 Ih for the same temperature range.
of normal and deuterated ice IKeywords: Ice Ih; lattice constants; thermal expansion.
In a previous paper we reported the lattice constants and h (Röttger et al., 1994). Synchrotron Xray powder diffraction data were used to obtain the lattice constants and unitcell volumes of H_{2}O and D_{2}O ice Ih in the temperature range 15–265 K. A polynomial expression was given for the unitcell 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 unitcell 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 Ih 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 manyterm polynomial expression was adopted to faithfully represent the measured data and not because there is a particular meaning in the various higherorder terms. We indicate that other approaches could be chosen based on various empirical quasiharmonic approximations (Reeber & Wang, 1996; Wang & Reeber, 1995) with a different set of parameters; the validity of these approximations for the ice Ih 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 Ih so clearly established by our data is still far from being understood (Herrero & Ramírez, 2011).
of normal and deuterated ice I

References
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Röttger, K., Endriss, A., Ihringer, J., Doyle, S. & Kuhs, W. F. (1994). Acta Cryst. B50, 644–648. CrossRef Web of Science IUCr Journals
Wang, K. & Reeber, R. R. (1995). J. Appl. Cryst. 28, 306–313. CrossRef CAS Web of Science IUCr Journals
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