On the mechanism of the zircon-reidite pressure induced transformation

Abstract

To cite this version:M. Marqués, J. Contreras-García, M. Flórez, J.M. Recio. On the mechanism of the zircon-reidite pressure induced transformation. Journal of Physics and Chemistry of Solids, Elsevier, 2009, 69 (9) This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting galley proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. A c c e p t e d m a n u s c r i p t.On the mechanism of the zircon-reidite pressure induced transformation M. Marqués, J. Contreras-García, M. Flórez, and J. M. RecioDepartamento de Química Física y Analítica, Universidad de Oviedo, E-33006Oviedo, Spain AbstractWe report first principles results of a detailed investigation directed to elucidate mechanistic aspects of the zircon-reidite phase transition in ZrSiO 4 . The calculated thermodynamic boundary is located around 5 GPa, and the corresponding thermal barrier, estimated from temperatures at which the transition is observed at zero and high pressure, is 133 kJ/mol. Under a martensitic perspective, we examine two different transition pathways at the thermodynamic transition pressure. First, the direct, displacive-like, tetragonal I4 1 /a energetic profile is computed using the c/a ratio as the tranformation parameter, and yields a very high activation barrier (236 kJ/mol). Second, a quasi-monoclinic unit cell allows us to characterize a transition path from zircon (β=90 • ) to reidite (β=114.51 • ) with an activation barrier of around 80 kJ/mol at β=104 • . This energy is somewhat lower than our previous estimation and supports the reconstructive nature of the transformation at the thermodynamic transition pressure.

Structure, elasticity and stability of reidite (ZrSiO4) under hydrostatic pressure: A density functional study

“…According to previous experimental studies performed under the ambient condition, zircon should have an indirect band gap of 6.5 eV [35], which provides the properties of good gate dielectric materials. Our LDA calculations, though underestimates the electronic band gap yielded a value 4.79 eV which agrees fairly well with earlier theoretical data [12]. The calculated band gaps of reidite and wolframite are 4.36 eV and 4.58 eV, respectively.…”

“…They suggested a transition to the wolframite type phase at 56 GPa. The transition T 1 leads to a significant volume collapse of 9.45% [12] in ZrSiO 4 structure, which is much less for the transition T 2 (2.43 %) (Fig. 6b).…”

“…It has led to a conclusive finding that zircon undergoes a first order reconstructive phase transition [12,13] at w8 GPa [45]. But, the stability of the reidite phase has remained virtually unexplored, and demands further attention to pressure induced polymorphic transformations of ZrSiO 4 .…”

Synthesis and magnetic properties of the high-pressure scheelite-type GdCrO4 polymorph

“…In fact, the more stable high-pressure polymorph of zircon crystallizes in the scheelite-type structure by reducing $ 10% the unit cell volume across the transition. This is believed to occur via a martensitic-phase transformation, that is, there exist a subtle but rapid rearrangement of atomic positions nonetheless in a cooperative way since the coordination of the A and B cations, bisdisphenoids-[AO 8 ] and tetrahedral- [BO 4 ] respectively, do not change through the transition [6,7]. However, the microscopic mechanism, that is, displacive or reconstructivemodel, remains highly controversial [6][7][8].…”

The high-pressure monazite-to-scheelite transformation in CaSeO4

“…Grzechnik et al, 2003), is a tetragonal 8À4 coordinated mineral found in hydrothermal veins and skarns, where it is commonly associated with wolframite and other large cation refractory minerals. The scheelite structure is shared by relatively few minerals; examples include stolzite, PbWO 4 , wulfenite, PbMoO 4 , powellite, CaMoO 4 and reidite, a high pressure ZrSiO 4 (zircon) polymorph that is found in impact breccias (Reid and Ringwood, 1969;Liu, 1979;Marques et al, 2009). Raspite is a polymorph of stolzite, but it is structurally unique with no other composition sharing its topology in any conditions (Fujita et al, 1977).…”