Related Experiment Video
Updated: May 30, 2026

Methods of Ex Situ and In Situ Investigations of Structural Transformations: The Case of Crystallization of Metallic Glasses
Published on: June 7, 2018
Cubic-tetragonal transition in KMnF(3): IR hard-mode spectroscopy and the temperature evolution of the (precursor)
Abstract:
Precursor effects were observed in KMnF(3) using infrared hard-mode spectroscopy. The intensity of the infrared-active mode near 265 cm(-1) follows the thermodynamic order parameter, Q, in the tetragonal phase (I4/mcm). An additional weak signal is found in the cubic phase ([Formula: see text]). The order parameter step at T(o) = 185.95 K (L = 0.129 J g(-1)) is smeared with excess intensity due to the tetragonal short range order extending to T>215 K. The intensity follows the predictions of Landau theory with a defect field G(defect) = -hQ, h = 6 J mol(-1). The observed excess intensities are compared with the appearance of precursor elastic softening. It is concluded that the precursor softening and the local tetragonal short range order are likely to be related to an extended defect structure, such as a tweed pattern, which may be stabilized by extrinsic defects.
Related Concept Videos
¹H NMR of Conformationally Flexible Molecules: Variable-Temperature NMR
¹H NMR of Conformationally Flexible Molecules: Temporal Resolution
IR Spectroscopy: Hooke's Law Approximation of Molecular Vibration
According to Hooke's law, the vibrational frequency is directly proportional to the...
IR Spectroscopy: Molecular Vibration Overview
Stretching vibrations are vibrational motions that occur along the bond line, changing the bond length or distance between two bonded atoms. They are further distinguished as symmetric or asymmetric. In symmetric stretching, the...
Atomic Spectroscopy: Effects of Temperature
At thermal equilibrium, the relative populations of excited and ground state atoms can be estimated using the Maxwell–Boltzmann distribution. For example, an increase in temperature from...
UV–Vis Spectroscopy: Molecular Electronic Transitions

