T. I. Maksimova

Electron paramagnetic resonance and optical spectroscopy of K3Na(CrO4)2 ferroelastics activated by MnO 4 2− molecular impurity ions

Crystals of a proper ferroelastic K3Na(CrO4)2 containing molecular impurity ions MnO42− are studied using electron paramagnetic resonance (EPR) and optical spectroscopy. The EPR spectrum of the Mn6+ ion contained in the molecular impurity ion MnO42− is identified at low temperatures (T ≤ 20 K). The intensity of this spectrum decreases unusually fast as the temperature increases. A broad IR luminescence band with a vibronic structure well resolved at a temperature of 8 K is revealed. Theoretical treatment of the Mn6+ ion involved in the molecular impurity ions MnO42− of the K3Na(CrO4)2 ferroelastic crystal suggests that an important role in this case is played by the pseudo-Jahn-Teller. The pseudo-Jahn-Teller effect offers an explanation for the appearance of a fine structure in the vibronic replicas in the luminescence spectrum, on the one hand, and accounts for the fast decrease in the intensity of the EPR spectrum of K3Na(CrO4)2: MnO42− with increasing temperature, on the other.

Photoinduced instability of MnO4- molecular defects in potassium iodide

Abstract An instability of the MnO4- molecular ion in KI is reported that occurs under intense resonant excitation in the 1A1 to 1T2 optical transition of the impurity. The intensities of the resonantly excited vibrational Raman lines and the absorption strength are used to monitor the time dependence of this effect which is investigated for different temperatures and excitation powers. A physical model is discussed that involves ionization of the molecular ion and qualitatively accounts for the experimental observations.

Manifestation of an intermediate phase in a ferroelastic K3Na(CrO4)2:MnO42− in raman and IR absorption spectra

In a broad temperature range of 4–300 K, we have performed a complex combined investigation of phase transitions in crystals of a ferroelastic K3Na(CrO4)2:MnO42− using methods of Raman light scattering and IR light absorption. Considerable changes that we have observed in both Raman and IR spectra in the range of T ≈ 150 K testify to the occurrence of another phase transition that has not been observed before at this temperature. We have performed a group-theoretical analysis and compared its results with experimental spectra, which has allowed us to conclude that there are two phase transitions in this crystal,

Origin of the structural local transition in the molecular impurity ion MnO42− in the K3Na(CrO4)2 ferroelastic

P\bar 3m1 \to C2/m \to C2/c

Resonant Raman scattering and photochromic effects in KI:MnO 4 −

, which occur at temperatures Tc1 ≈ 230 K and Tc2 ≈ 150 K, respectively.

Soft mode mechanism of the transition into the low-temperature ferroelastic phase in K3Na(CrO4)2 crystals

This paper reports on the first study in K3Na(CrO4)2 crystals of Raman spectra within a broad temperature interval of 4–300 K. The study has revealed significant variations in the intensity and shape of the Raman lines at T = 150 K; a group theory analysis has revealed that the structural phase transition in this ferroelastic proceeds in two stages through an intermediate phase:

Soft mode mechanism of the transition into the low-temperature ferroelastic phase in K-=SUB=-3-=/SUB=-Na(CrO-=SUB=-4-=/SUB=-)-=SUB=-2-=/SUB=- crystals

P\bar 3m1 \to C2/m \to C2/c