Residual stress induced crystalline to amorphous phase transformation in Nb2O5 quantum dots

Abstract

Nb2O5 quantum dots (QDs) were grown using a simple technique of vacuum thermal evaporation. QDs were found to be crystalline in nature by selected area electron diffraction (SAED) in TEM. Samples with thickness up to 20 nm did not show any significant residual strain. Residual stress effect on band gap of crystalline Nb2O5 was studied for films thicker than 20 nm. Residual strain was determined using SAED of the films with reference to powder X-ray diffraction (XRD). Films thicker than 45 nm become amorphous as analyzed by both SAED and XRD. The optical absorption of films in the range 25–60 nm indicates significantly varying optical band gap of films. The varying band gap with film thickness scales linearly very well with the variation of residual stress with film thickness. The residual stress dependence of band gap of crystalline films yields stress free band gap as 3.37 eV with pressure coefficient of band gap (∂Eg/∂P)T = −29.3 meV/GPa. From this study, the crystalline to amorphous transformation in tetragonal form of M-Nb2O5 has been determined to be at about 14 GPa. Both pressure coefficient of band gap and crystalline to amorphous transition for tetragonal M-Nb2O5 have been determined for the first time in the literature.

Elastic Behavior of Nb2O5/Al2O3 Core–Shell Nanowires in Terms of Short-Range-Order Structures

“…As a result of the measured NWs, an average value of 67 ± 10 GPa was determined. This value for Young’s modulus is in agreement with the published data concerning Nb 2 O 5 thin films, however, differs significantly from the available data on Nb 2 O 5 NWs …”

“…As a result of the measured NWs, an average value of 67 ± 10 GPa was determined. This value for Young's modulus is in agreement with the published data concerning Nb 2 O 5 thin films, 59 however, differs significantly from the available data on Nb 2 O 5 NWs. 34 For a Nb 2 O 5 /Al 2 O 3 core−shell NW with a shell thickness of 10 nm, as shown in Figure 8, a value of 67 GPa was chosen for Young's modulus of the Nb 2 O 5 core and a value of 160 GPa for the Al 2 O 3 shell.…”

“…To begin with, values for the Young’s moduli of Nb 2 O 5 and Al 2 O 3 were taken from literature. Studies on Nb 2 O 5 thin films have reported values of 70 GPa or higher, 100–200 GPa, for the Young’s modulus depending on the deposition technique. Varghese et al investigated Nb 2 O 5 NWs synthesized by thermal oxidation using an AFM three-point bending test and reported Young’s moduli between 5 and 30 GPa depending on the NW diameter .…”

Stoichiometric Layered Potassium Transition Metal Oxide for Rechargeable Potassium Batteries

“…In addition, as Cr 3+ is oxidized, some of the strong ligand field stabilization for the octahedral site is removed, creating a large driving force for a collapse of the structure. In addition, the large size difference of Cr 6+ and Cr 3+ in the Cr layers can lead to mechanical stress, resulting in a crystalline-to-amorphous transition when the stress is accumulated, as often observed in metal oxides and silicon. − …”

Pressure induced transformation and subsequent amorphization of monoclinic Nb2O5 and its effect on optical properties

“…Table 1 lists the refined parameters for the monoclinic (1.8 GPa) and orthorhombic (9.9 GPa) phases. With further increasing pressure, most diffraction peaks disappear at 21.4 GPa, except the two broad bands at approximately 3.0 Å and 3.4 Å, which are associated with an amorphous phase [44,45]. Subsequently, the two broad bands are further broadened and weakened with increasing pressure, yet still detectable up to a pressure of 28.7 GPa.…”