On the transformation pathways of alpha-PbO2-type TiO2 at the twin boundary of rutile bicrystals and the origin of rutile bicrystals

Abstract

Extraction and electron irradiation (under transmission electron microscopy) of an epitaxial nanometer-thick [-PbO 2-type TiO 2 slab between twinned rutile bicrystals in ultra-high pressure metamorphic rock caused phase changes into a modified fluoritetype and then an amorphous phase. This martensitic-type transition process accounts for the dislocations and stacking faults of the slab and disordering of Ti in the adjoined rutile bicrystals. Additional hydrothermal experiments of sol-gel TiO 2-Al 2 O 3 performed at 8.5-9 kbar and 675-800°C in the piston-cylinder apparatus indicated that twinned rutile bicrystals were shaped in mirror image without the formation of [-PbO 2-type TiO 2 slab at the twin boundary and with no other planar defects for the bicrystals. The twinned bicrystals can be rationalized by growth and/or coalescence processes. Accordingly, it is not justified to assume a precursor phase of [-PbO 2-type structure for twinned rutile bicrystals when there is no such relic. Rutile, unless exsolved epitaxially from a host mineral such as garnet, does not constitute evidence for unusually deep burial for ultra-high pressure terranes.

Controlling the Thermoelectric Properties of Nb-Doped TiO2 Ceramics through Engineering Defect Structures

“…Figure a is a TEM bright-field image of TN60, showing two slender, needle-shaped twins inside the grain. Figure b,c shows the experimental and simulated SAED patterns obtained along the ⟨111⟩ R zone axis in Figure a, showing typical diffraction patterns for a twin structure. − The blue circles mark the reflection spots from the main twin domain, the red circles mark the reflection spots for a second twin domain, and the yellow circles mark the reflection spots of the (01̅1) twin plane for both twin domains. The reflection spots in the simulated SAED patterns match those in the experimental SAED patterns very well, although the intensities are different.…”

Exsolution of rutile or apatite precipitates surrounding ruptured inclusions in garnet from UHT and UHP rocks

“…Exsolution (precipitation) of rutile out of garnet is perhaps the most commonly proposed mechanism (e.g. Griffin et al ., ; Smith & Dawson, ; Larsen et al ., ; Zhang & Liou, ; van Roermund et al ., ; Zhang et al ., ; Song et al ., ; Shen et al ., ; Liu et al ., ; Ague & Eckert, ; Proyer et al ., ). The Ti content of garnet increases in a general way with temperature or pressure (e.g.…”

“…Oriented rutile (±ilmenite) needles are commonly found as inclusions in garnet within rocks from high or extreme pressure and/or temperature environments. They are present, for example, in rocks from many high‐pressure (HP) and ultrahigh‐pressure (UHP) localities, including the Western Gneiss Region (Larsen et al ., ), the Dabie‐Sulu terrane (Zhang & Liou, ; Ye et al ., ; Zhang & Liou, ; Malaspina et al ., ), the Saxonian Erzgebirge (Massonne, ; Hwang et al ., ), the Greek Rhodope (Mposkos & Kostopoulos, ), the Bohemian Massif (O'Brien & Rötzler, ; Hwang et al ., ; Vrana, ), the diamondiferous granulite of Cueta, Betic‐Rif cordillera, Spain (Ruiz‐Cruz & De Galdeano, ), the Kokchetav Massif (Shen et al ., ), the Ngoc Linh Complex (Osanai et al ., ) and the Palghat–Cauvery suture zone (Sajeev et al ., ). Furthermore, oriented rutile needles are found in garnet of ultrahigh‐temperature (UHT; >900 °C) granulites and high‐ P granulites, including the Central Maine terrane (CMT) of northeastern Connecticut (CT; Ague & Eckert, ), the Snowbird tectonic zone (Snoeyenbos et al ., ), the Gory Sowie Massif (O'Brien et al ., ), the Central Schwarzwald Gneiss Complex (Marschall et al ., ) and the Tuguiwula Khondalite Belt (Liu et al ., ).…”

Phason strained quasicrystalline and crystalline precipitates in Zr–Al–Ni–Cu–Nb bulk metallic glass matrix composites

“…The oxidation may come into being during the melting or annealing. 10 1 À Á twinning of rutile is common in natural rock and can crystallize during hydrothermal/solid-state high-temperature experiments [29,30]. The oxygen and the transition metal Ti contamination may stabilize the formation of quasicrystal phase in Zr-base BMG [31][32][33][34] besides that the TiO 2 inclusions themselves can influence the mechanical properties of the BMG matrix composites.…”