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Low temperature thermal diffusivity of LiKSO4 obtained using the photoacoustic phase lag method
Jorge, M.P.P.M.;Vieira, M.M.F.;Mendes Filho, J.;Oliveira, A.C.;Vieira Jr., N.D.;Morato, S.P.;
Materials Research , 1999, DOI: 10.1590/S1516-14391999000100007
Abstract: this paper describes the determination of the thermal diffusivity of likso4 crystals using the photoacoustic phase lag method, in the 77 k to 300 k temperature interval. this method is quite simple and fast and when it is coupled to a specially designed apparatus, that includes a resonant photoacoustic cell, allows for the determination of the thermal diffusivity at low temperatures. the thermal diffusivity is an important parameter that depends on the temperature, and no values of this parameter for likso4, at low temperature, have yet been reported. the likso4 is a crystal with many phase transitions which can be detected via the anomalies in the variation of the thermal diffusivity as a function of the temperature.
Low temperature thermal diffusivity of LiKSO4 obtained using the photoacoustic phase lag method
Jorge M.P.P.M.,Vieira M.M.F.,Mendes Filho J.,Oliveira A.C.
Materials Research , 1999,
Abstract: This paper describes the determination of the thermal diffusivity of LiKSO4 crystals using the photoacoustic phase lag method, in the 77 K to 300 K temperature interval. This method is quite simple and fast and when it is coupled to a specially designed apparatus, that includes a resonant photoacoustic cell, allows for the determination of the thermal diffusivity at low temperatures. The thermal diffusivity is an important parameter that depends on the temperature, and no values of this parameter for LiKSO4, at low temperature, have yet been reported. The LiKSO4 is a crystal with many phase transitions which can be detected via the anomalies in the variation of the thermal diffusivity as a function of the temperature.
Phase transitions in layered crystals  [PDF]
Yuri Mnyukh
Physics , 2011,
Abstract: It is demonstrated by analyzing real examples that phase transitions in layered crystals occur like all other solid-state phase transitions by nucleation and crystal growth, but have a specific morphology. There the nucleation is epitaxial, resulting in the rigorous orientation relationship between the polymorphs, such that the direction of molecular layers are preserved. The detailed molecular mechanism of these phase transitions and formation of the laminar domain structures are described and related to the nature of ferroelectrics.
Image Analysis Studies for Phase Transitions of Ferroelectric Liquid Crystals  [PDF]
S. Sreehari Sastry,B. Gowri Sankara Rao,K. B. Mahalakshmi,K. Mallika,C. Nageswara Rao,Ha Sie Tiong
ISRN Condensed Matter Physics , 2012, DOI: 10.5402/2012/423650
Abstract: Phase transition temperatures of ferroelectric liquid crystals ((S)-(-)-2-methylbutyl 4′-(4″-n-alkanoyloxybenzoyloxy) biphenyl-4-carboxylates (where and 18)) are studied through two techniques of image analysis. One is a statistical method, applied to compute the statistical parameters from the textures of each sample and the other, computation of Legendre moments being applied as image moment analysis, both of which are considered as a function of temperature. The textures of the samples are recorded with the polarizing optical microscope (POM) attached to the hot stage and high resolution camera. The phase transition temperatures of samples are inferred by the abrupt changes in the computed parameter values. The results obtained from the present methodology are in good agreement with those published in earlier literature done by the different techniques, like differential scanning calorimetry (DSC). 1. Introduction The studies on phase transitions in thermotropic liquid crystal have seen considerable progress since 1980 [1]. With the availability of high resolution and sensitive experimental techniques, it could be made easy to record precisely the transformations that occur during mesophase changes. Identification of transition phases and transition temperatures is the vital aspect to characterize the properties of liquid crystal compounds. Besides, the ordering in phase transitions, namely, first-order/second-order phases, is crucial in current liquid crystal field studies [2–4]. With its wide applications in the use of optical switches, light valves, display and storage devices, and other electrooptic devices, in particular the study on the ferroelectric liquid crystals (FLCs) has generated much interest for synthesizing and characterizing the new FLCs [5–9]. Having these objectives, the present attempt is aimed to study the transition temperatures of the two synthesized ferroelectric liquid crystals ((S)-(-)-2-methylbutyl 4′-(4′′-n -alkanoyloxybenzoyloxy) biphenyl-4-carboxylates (where and 18)) through the image analysis techniques, statistical and image moments approaches applied to the microscopic textures of FLCs. The results of the study are compared with those of published earlier studies [10]. Also this kind of work was done for room temperature liquid crystals, cholesteric liquid crystals, and for discotic liquid crystals [11–15]. 2. Experimental The liquid crystals of chiral esters (S)-(-)-2-methylbutyl 4′-(4′′-n-alkanoyloxybenzoyloxy) biphenyl-4-carboxylates where and 18 having different alkyl chain lengths are synthesized [10] and used.
Thermodynamics and dielectric anomalies of DMAAS and DMAGaS crystals in the phase transitions region (Landau theory approach)  [PDF]
I. V. Stasyuk,O. V. Velychko,Z. Czapla,R. Czukwinski
Physics , 2000,
Abstract: A simple description of thermodynamics of DMAAS and DMAGaS ferroelectric crystals by means of Landau expansion is proposed. Conditions of occurrence of phase transitions are established and their temperatures are obtained. The influence of external hydrostatic pressure on phase transitions is described. The temperature behaviour of dielectric susceptibility components and their anomalies in the vicinity of phase transition points are investigated. Obtained results are compared with experimental data.
Photoacoustic wave propagating from normal into superconductive phases in Pb single crystals  [PDF]
Masanobu Iwanaga
Physics , 2005, DOI: 10.1103/PhysRevB.72.012509
Abstract: Photoacoustic (PA) wave has been examined in a superconductor of the first kind, Pb single crystal. The PA wave is induced by optical excitation of electronic state and propagates from normal into superconductive phases below T$_{\rm C}$. It is clearly shown by wavelet analysis that the measured PA wave includes two different components. The high-frequency component is MHz-ultrasonic and the relative low-frequency one is induced by thermal wave. The latter is observed in a similar manner irrespective of T$_{\rm C}$. On the other hand, the MHz-frequency component is obviously enhanced below T$_{\rm C}$. The behavior is reproduced by the change of attenuation of longitudinal ultrasonic wave and is consistent with BCS theory.
Transition Temperatures of Thermotropic Liquid Crystals from the Local Binary Gray Level Cooccurrence Matrix  [PDF]
S. Sreehari Sastry,T. Vindhya Kumari,C. Nageswara Rao,K. Mallika,S. Lakshminarayana,Ha Sie Tiong
Advances in Condensed Matter Physics , 2012, DOI: 10.1155/2012/527065
Abstract: This paper presents a method which combines the statistical analysis with texture structural analysis called Local Binary Gray Level Cooccurrence Matrix (LBGLCM) to investigate the phase transition temperatures of thermotropic -alkyloxy benzoic acid ( OBA, and 12) liquid crystals. Textures of the homeotropically aligned liquid crystal compounds are recorded as a function of temperature using polarizing optical microscope attached to the hot stage and high resolution camera. In this method, second-order statistical parameters (contrast, energy, homogeneity, and correlation) are extracted from the LBGLCM of the textures. The changes associated with the values of extracted parameters as a function of temperature are a helpful process to identify the phases and phase transition temperatures of the samples. Results obtained from this method have validity and are in good agreement with the literature. 1. Introduction Thermotropic liquid crystals exhibit a variety of phases and phase transitions in the materials [1–3]. The structure of thermotropic liquid crystal phases is easily influenced by external conditions, for example, the properties of the surface of a microscope cover glass. In case of planar alignment of LC’s the phases can possess complex structures and properties which are studied from several decades. In contrast, the investigation of liquid crystals as components in heterogeneous and its anchoring homeotropically is still in an early stage, especially when the more complex phases such as different smectic phases are considered. The understanding of textures and their characteristic features of thermotropic liquid crystal is the main focus of our studies to investigate the phase transitions [4]. There are several techniques used to identify the mesophases or phase transitions of liquid crystals, such as polarizing optical microscope (POM), differential scanning calorimetry (DSC), differential thermal analysis (DTA), and X-ray diffraction. POM is one of the essential tools for the characterization of newly synthesized mesogenic materials, together with DSC, DTA, and X-ray investigations. While DSC and DTA are easily and quickly carried out methods, they merely provide information on phase transition temperatures, heat of transitions, heat capacity of various phases, and the order of the transitions. X-ray investigations for determination of the phase type have to be performed on macroscopically well-oriented samples which is often time consuming and sometimes hard to realize. However, precise phase identification could not easily be made by DSC,
Phase Transitions and Quantum Stabilization in Quantum Anharmonic Crystals  [PDF]
Alina Kargol,Yuri Kondratiev,Yuri Kozitsky
Physics , 2007, DOI: 10.1142/S0129055X08003353
Abstract: A unified theory of phase transitions and quantum effects in quantum anharmonic crystals is presented. In its framework, the relationship between these two phenomena is analyzed. The theory is based on the representation of the model Gibbs states in terms of path measures (Euclidean Gibbs measures). It covers the case of crystals without translation invariance, as well as the case of asymmetric anharmonic potentials. The results obtained are compared with those known in the literature.
The nature of transitions and generation mechanisms in optically homogeneous CdS crystals
Garkavenko A. S.
Tekhnologiya i Konstruirovanie v Elektronnoi Apparature , 2012,
Abstract: The research has shown that the optimum laser transitions in electronic excitation lasers based on radiation doped, optically homogeneous CdS crystals are the transitions from the degenerate conduction band to shallow acceptor levels of palladium and silver isotopes.
On the problem of phase transitions in lysozyme crystals  [PDF]
Yu. Vasylkiv,Yu. Nastishin,R. Vlokh
Physics , 2007, DOI: 10.3116/16091833/8/2/83/2007
Abstract: We present experimental evidence of the fact that lysozyme crystals, which are grown from their mother solution and exist in it, dissolve on heating above T=307 K. We argue that the anomaly in the light scattering recently observed at the temperature T=307 K and identified in the reference [Svanidze A. V. et al. 2006. JETP Lett. 84: 551] as a structural crystalline phase transition in the single lysozyme crystals, in fact, corresponds to a temperature limit of the crystal existence.
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