Phase Transitions In LiKSO4 Research Articles

Analysis of the peak position and linewidth as a function of temperature for the phase transitions in LiKSO4

Analysis of the peak position and the linewidths of various infrared modes is performed at high (300–850 K) and low (1.5–300 K) temperatures using the experimental data from the literature for LiKSO4 which exhibits a sequence of phase transitions. The temperature dependences of the frequency and the linewidth which are derived from the anharmonic self-energy are fitted to the observed peak positions and the linewidths of the S–O stretching modes (internal [Formula: see text] modes at 1135 cm[Formula: see text] and at 1180 cm[Formula: see text]), peak position of the S–O bending [Formula: see text] (internal) modes, the peak position and the linewidth of the Li mode at 429 cm[Formula: see text] (external mode), and of the infrared band at 363 cm[Formula: see text] for LiKSO4. Our calculated peak positions and the linewidths, which are in good agreement with the observed data show that the anharmonic self-energy model describes adequately the observed behavior of the successive phase transitions in LiKSO4.

Phase Transitions in LiKSO4 between 10 and 750 K

The phase behavior of LiKSO4 single crystals was studied by several techniques: ac calorimetry, differential scanning calorimetry (DSC) and impedance spectroscopy. Our results show distinct phase transitions at 38, 57, 206 and 718 K on cooling run. In the vicinity of 57 K new anomalous changes both in the specific heat and the dielectric constant were observed on cooling runs. The phase transitions showed a thermal hysteresis on successive heating and cooling cycles and a strong thermal hysteresis was observed by impedance spectroscopy in the phase transition reported at 206 K on cooling run. A comprehensive discussion of these results, together with those of previous works using the same as well as different techniques, leads to a better understanding of the observed phase behavior in LiKSO4.

Thermal Analysis and X-Ray Diffraction Study on LiKSO4: A New Phase Transition

Results of a detailed X-ray diffraction and thermal analysis study of the structural phase transitions in LiKSO4 carried out in the temperature range 123–1000 K are presented. The study indicates five phase transitions in the temperature range studied at 937, 707, 226 (268), 200 (251), and 186 (190) K (values in parentheses are for a warming process). The transition at 226 (268) K is reported for the first time. The different phases (from high to low temperature) show the space groups P63/mmc, P21cn, P63, P63mc, P31c, and Cmc21. The working conditions allowed us to obtain the different phases without twin crystals and without mixtures of several phases. We were thus able to determine the crystal structures of the different phases with more accuracy. The transitions at high temperature produce large variations in the crystal structure and the enthalpy of process is high, while at low temperature, as the structure is more compact, an activation energy is necessary, and the transitions show a thermal hysteresis, while the structural variation is as small as the enthalpy of the process.

Low-temperature sequence of phase transitions in LiKSO4 studied by EPR.

The low-temperature sequence of phase transitions in ${\mathrm{LiKSO}}_{4}$ has been studied by EPR using the paramagnetic center ${\mathrm{Tl}}^{2+}$. The coexistence of different phases in some temperature ranges is demonstrated. An axial-symmetry phase has been observed at 77 K after a fast cooling process. The ferroelastic phase (below 190 K) has been studied by applying uniaxial pressure. The existence of twinnings within each ferroelastic domain and a monoclinic-symmetry structure for this phase are found. A tilting of the paramagnetic tensors has been observed below 190 K, reflecting the freezing of the sulfate-ion orientational disorder. A model for the ferroelastic structure is proposed.

Visual observation of phase transitions in LiKSO4 under pressure

Phase transitions in LiKSO4 have been visually observed in a diamond-anvil cell up to 16 GPa. The observations confirm a symmetry change at 0·9 GPa and a solidstate crystal to amorphous transition at 12 GPa. The crystal exhibits a memory across the crystalline transitions. Interesting microstructural features were observed in the range of the amorphous phase.

Phase transitions in LiKSO4: Low-temperature neutron diffraction results

Abstract Results of a detailed crystallographic study of the structural phase transitions in LiKSO4, carried out using single crystal neutron diffraction at ambient and below-ambient temperatures (300–100 K), are presented. The study indicates two clear phase transitions at 205 K (from space group P63 to space group P31c), at 189 K (to space group Cc) and a third transition at about 130 K in the cooling cycle. The corresponding temperatures are 250 K, 200 K and 138 K in the heating cycle. The existence of twins, mixed phases, and extremely sluggish kinetics for the various phase transitions, as well as the structural details of the various phases in this mixed salt, can explain the apparent inconsistencies in the results of several experimental investigations reported in the literature.

On the ferroelastic phase transition in LiKSO4: Brillouin scattering studies from 140 to 300 K and Landau theory modelling

The authors report on the results of Brillouin scattering studies of single crystals of ferroelastic LiKSO2 in the range of temperatures from 140 to 300 K. They have measured all the nonzero second-order elastic constants and found them to be essentially temperature-independent except for c66. The interesting hysteretic temperature dependence of c66, its incomplete softening at the transition temperature and other physical properties of LiKSO4 previously reported have motivated them to re-examine and extend the theoretical models adopted earlier. A Landau expansion of the free-energy involved strain components including spontaneous strain, polarisation and both order parameters for the two neighbouring transitions around 190 and 250 K. As a result of this analysis they have obtained good qualitative agreement with the reported experimental data.

Universal scaling law for first order phase transformation: LiKSO4

We have measured the kinetics of phase transition in LiKSO4 (C 6 6 →C 3v 4 ;T c∼201 K) by monitoring the time-dependent change in Raman intensity of selected vibrational lines at various temperatures in the transformed phaseC 3v 4 . We find that the observed growth curves for several temperatures display a nearly universal shape when plotted against a suitably scaled time parameter. We interpret our results in terms of a phenomenological model of nucleation and growth.

Absence of unusual sequence of commensurate-incommensurate phase transitions in LiKSO4: an EPR study using an SO4-probe

The structural phase transitions in LiKSO4 have been examined by EPR, at X band, using a paramagnetic SO4- probe. The orientation of the SO4- probe ion is modified with respect to that of the parent SO42- ion. The authors show that this modified orientation and its temperature-dependent motion has misled earlier workers into suggesting an unusual sequence of commensurate-incommensurate transitions in LiKSO4. Their measurements also support the occurrence of another transition in this compound at 130 K, as predicted by neutron diffraction work. This transition appears to trigger an anti-ferro-distortion resulting in the rotation of SO4- by +or-10 degrees about the c axis; all of the sulphates remain chemically equivalent. LiKSO4 exists below 130 K as a mixed-phase compound down to 77 K.

EPR studies of the low-temperature phase transition in LiKSO4 by SO4− and CRO43− centres

EPR studies of the low-temperature phase transition in LiKSO4 by SO4− and CRO43− centres

Kinetics and symmetry changes in low-temperature phase transitions in LiKSO4

The kinetics and the symmetry changes associated with the low-temperature structural phase transitions in LiKSO4 have been investigated by single crystal neutron diffraction. The study indicated three clear phase transitions at 205 K (from sp. gr. P63 to sp. gr. P31c), at 189 K (to sp. gr. Cc) and 135 K in the cooling cycle; a phase change is also indicated at 165 K. All these transitions show thermal hysteresis. The full crystal does not undergo transformation at any of the transition temperatures but exhibits mixed phases. The kinetics of the phase transitions are characterised by prolonged equilibration times (days) which strongly depend on the thermal history of the sample. With the results of the structural investigations in the temperature range 300 K to 100 K, an attempt has been made to explain the anomalies and variant results observed in the physical properties of LiKSO4 at low temperatures.

Detection of ferroelastic phase transition of LiKSO4 crystal by depolarization of transmitted light

A new method to detect multidomain phase transition by measuring the depolarization of transmitted light is reported. As an example, the ferroelastic phase transition in LiKSO4 was investigated in more detail. It was found that the multidomain phase F3 was ferroelastic. More accurate transition temperatures between phases F2 and F3 in cooling and heating cycle were determined to be -85°C and -79°C respectively.

Powder neutron diffraction study of low temperature phase transition in LiKSO4

Abstract The salient features of the neutron diffraction measurements on polycrystalline sample of LiKSO4 at 170 K and 104 K are reported. The sample undergoes a phase transformation to a single phase as against “mixed phases” reported in single crystal studies. These differences are discussed on the basis of the kinetics of nucleation and growth processes.

Effect of heating rate on the phase transition in LiKSO4

Effect of heating rate on the phase transition in LiKSO4

Low-temperature phase transitions in LiKSO4: a neutron diffraction study

Low-temperature phase transitions in LiKSO₄: a neutron diffraction study