Eine neue Hochtemperaturform von TiO: HTiO

Abstract

Mit CO2‐LASER‐Technik wurden bei Temperaturen oberhalb 3 000°C Einkristalle einer Hochtemperaturform von TiO (HTiO) dargestellt. Sie kristallisieren mit einer an Oxiden des zweiwertigen Titans bisher nicht beobachteten Kristallstruktur, isotyp zu Wolframcarbid, mit Ti2+ in trigonal prismatischer Sauerstoffumgebung. Raumgruppe D 3h1P6m2; a = 3,0310; c = 3,2377 Å; Z = 1.

Stability of vacancy-free crystalline phases of titanium monoxide at high pressure and temperature

“…On compression, c/a increases and reaches 1.5% at 50 GPa, where this phase is equilibrium. For the phase H-TiO, only the results of experimental measurements [20] are available, and the measured atomic volume noticeably exceeds the calculated value. We recall that the experiment [20] has been performed by using the laser heating technique at very high temperature and so the H-TiO phase has been fabricated in highly non-equilibrium conditions.…”

“…For the phase H-TiO, only the results of experimental measurements [20] are available, and the measured atomic volume noticeably exceeds the calculated value. We recall that the experiment [20] has been performed by using the laser heating technique at very high temperature and so the H-TiO phase has been fabricated in highly non-equilibrium conditions. According to our calculations, each of the three considered phases of TiO are rather poor metals, with a pseudogap at the Fermi level [14].…”

“…However, the search in a wide pressure range from 0.1 MPa to 100 GPa demonstrates that the phase ε-TiO remains stable up to 28 GPa and above this pressure, the denser phase H-TiO becomes the ground state. In should be noted that both stable phases, ε-TiO and H-TiO, are synthesized in chemical reactions from melts at atmospheric pressure [19,20] and not observed experimentally on 'suppression' of vacancies in B1-derived structures.…”

“…Even more unexpected turned out the results of the experiment [19], where a new defect-free phase ε-TiO isotypic to ε-TaN was synthesized at normal pressure by using a bismuth flux. Another defectfree phase denoted as H-TiO was prepared above 3000°C by CO 2 -laser technique [20], but it was originally considered as highly metastable and not discussed in subsequent works.…”

ɛ‐TiO, a Novel Stable Polymorph of Titanium Monoxide

“…Here, the Ti and O vacancies alternate in every third (110) plane of the NaCl‐type structure. Another hexagonal type of TiO, H‐TiO, ( P m 2, a= 3.0310(6) Å, c= 3.2377(9) Å) has been synthesized above 3273 K, and it is isostructural with WC because the Ti atoms are located in sixfold coordination sites of oxygen trigonal prisms. Herein, a new polymorph of titanium monoxide, ɛ‐TiO, has been prepared by using a Bi flux.…”