**5. Conclusions**

Accurate thermal expansion coefficients were measured for sol-gel products of stoichiometric MgTiO3. The lattice parameters of MgTiO3 made by sol-gel synthesis measured in HT-XRD between 25 and 890 ◦C are well integrated with the previously reported HT-XRD study of sol-gel MgTiO3 product between 700 and 1300 ◦C. The lattice parameters of stoichiometric MgTiO3 sol-gel products are slightly lower than nonstoichiometric MgTiO3 with maximal excess of Ti. It is assumed the TECs of geikielite depend on deviations from stoichiometry. Neither sample preparation nor diffraction method modified the TECS in geikielite.

**Author Contributions:** T.T., student coordinator, literature survey, cross-checking all XRD results; G.K., R.T., XRD analysis of all XRD by Fullprof; B.A.R., collected the high-temperature XRD and performed the Rietveld analysis in Topas; J.Z., samples' production by sol-gel technique; H.D. and R.Z.S. synthesis of samples. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research received no external funding.

**Acknowledgments:** The authors wish to acknowledge Elena Goncharov for the contribution to the synthesis.

**Conflicts of Interest:** The authors declare no conflict of interest.
