Pressure-Induced Phase Transition in Mn(Ta,Nb)₂O₆: An Experimental Investigation and First-Principle Study

Abstract

The high-pressure and high-temperature behaviors of manganotantalite Mn­(Ta,Nb)2O6 have been investigated by single-crystal X-ray diffraction and Raman spectroscopy combined with diamond anvil cell technique, as well as first-principle calculations. A pressure-induced reversible phase transition of manganotantalite occurs at 9.5 GPa and room temperature, accompanied by a large volume collapse (∼7.0%) and drastic color change from brownish-yellow to red. The space groups of low-pressure (LP) and high-pressure (HP) phases are the same (Pbcn), but the coordination numbers of Mn increase from six to eight and Ta increase from six to seven, respectively. The band gap becomes narrow from 2.37 to 1.59 eV. We determined the P-T phase diagram of manganotantalite with a positive Clapeyron slope of dP/dT = 0.0073 GPa/K. The P-V data were fitted to a second-order Birch–Murnaghan equation of state with B 0 = 149(4) GPa for the LP phase and B 0 = 188(3) GPa for the HP phase. The isothermal Grüneisen parameters were determined to be 0.23∼2.03 of the LP phase and 0.59∼0.86 of the HP phase for Raman modes. High-pressure behaviors of Mn­(Ta,Nb)2O6 indicate that this kind of material is a potential effective pressure sensor to monitor pressure change or warn pressure abnormality.

Phase Transitions in Natural Vanadinite at High Pressures

“…This was verified by a drastic color change from reddish (reddish for naked eye but orange in the photo taken by Leica microscope with Sony camera due to the whitebalance setting) to transparent during decompression after the experiments (Figure 3b), indicative a reversible phase transition at ~26.2 GPa. Similar phenomena were observed in many compounds upon compression, i.e., KTb(MoO4)2 [45], siderite [46], and manganotantalite [47]. Jayaraman et al [45] attributed the color change of KTb(MoO4)2 to 4f-5d transition in Tb initiated by the structural transition, and consequent intervalence charge transfer between Tb and Mo.…”

“…Müeller et al [46] associated the transparent-green color change of siderite to the spin transition. Liu et al [47] explained the phenomenon by the alteration of electronic structure properties and a narrowing of band gap in Mn(Ta,Nb) 2 O 6 . It is anticipated that the transparent-reddish color change of vanadinite observed in this study likely results from the energy level splitting of transition element V. Future experiments and theoretical calculations are necessary to fully understand the character of reversible pressure-induced color changes in vanadinite.…”

Pressure-driven multiple optoelectronic evolution in CsMoO3(IO3) with dual functional [MoO6] and [IO3] groups

“…[16][17][18][19] Currently, an effective approach to obtain materials with intriguing optoelectronic properties under pressure is to alter localized functional groups. 20 For example, prior studies point out that pressure can change the configurations of lonepair and second-order Jahn-Teller functional groups, [21][22][23] which further induce novel optoelectronic phenomena, such as the switching of the SHG effect, 24 the enhancement of photocurrent response, 25,26 the transformation of the bandgap, 27,28 and so on. It is worth noting that many of these reports generally achieve simple optoelectronic property changes through the modulation of a single functional group.…”

Determination of the tricritical point, H–T phase diagram and exchange interactions in the antiferromagnet MnTa2O6

“…In AB 2 O 6 compounds usually A and B sites are occupied by divalent and pentavalent cations respectively, forming octahedra [AO 6 andBO 6 ] with six oxygen atoms [3,5]. These compounds have potential applications in the field of satellite and mobile communications as dielectric resonators and filters [6,[10][11][12], as electrochemical gas sensors [6,13], and in supercapacitors [6,12].…”