Electrical Phase Transition Research Articles

Electrical properties and phase transitions in ethylenediammonium dinitrate

dc and ac electrical conductivities, dielectric constant and dielectric loss factor in single crystals of ethylenediammonium dinitrate (EDN) have been measured axiswise as a function of temperature. All the above properties exhibit anomalous variations at 404 K thereby confirming the occurence of a phase transition in EDN at this temperature. Electrical conductivity parameters have been evaluated and possible conduction mechanisms are discussed. The role of protons in electrical trasport phenomenon is established by chemical analysis.

Electrical conductivity, dielectric constant and phase transitions in pure and doped diammonium hydrogen phosphate

DC and AC electrical conductivity measurements in single crystals of diammonium hydrogen phosphate along the c axis show anomalous variations at 174, 246 and 416 K. The low-frequency dielectric constant also exhibits peaks exactly at these temperatures with a thermal hysteresis of 13 degrees C for the peak at 416 K. These specific features of the electrical properties are in agreement with earlier NMR second-moment data and can be identified with three distinct phase transitions that occur in the crystal. The electrical conductivity values have been found to increase linearly with impurity concentration in specimens doped with a specific amount of SO42- ions. The mechanisms of the phase transition and of the electrical conduction process are discussed in detail.

Electrical conduction behavior and phase transition of CaO-stabilized ZrO 2

Phase transition temperatures of 13 and 15 mol% CaO-stabilized ZrO 2 were determined on the basis of their conduction behavior. Four-terminal dc conductances of sintered samples at 1560-990°C, R −1, were measured at 10°C intervals. These conductance measurements were carried out after the samples had been annealed for 1–72 h at each temperature. Constants a, b and c were evaluated by fitting the following equation to the conductance data: ln R −1 T= a( T −1) 2+ b( T −1)+ c. The conductance at each temperature was calculated using the constants and, subsequently, the degree of deviation of the observed conductance from the calculated conductance, D, was evaluated: D=(observed R −1−calcd. R −1)/(calcd. R −1). By plotting the D against temperature, peaks corresponding to respective phase transitions were obtained.

Effect of Deuteration on the Electrical Conductivity, Dielectric Constant, and Phase Transition in (NH4)3H(SO4)2

Measurements of dc conductivity and dielectric constant show that deuteration causes an upward shift of the high tem­ perature phase b'ansition point from 186.5 to 191°C and a downward shift of the low temperature transition point from 10 to -1.5°C in LiNa.S04. Mechanisms of phase transitions and of electrical transport in the crystal are discussed.

Conventionally Sintered (Na0.5,K0.5)NbO3 with Barium Additions

The effect of Ba additions on sodium potassium niobate (NKN) ceramic bodies was investigated with regard to sintering behavior, densification, and electrical properties. Small additions of Ba retard grain growth and increase density. The approximate solubility limit of Ba is 1.5 mol%. During firing the loss of Na and K was very low. Both electrical phase transitions in NKN are lowered with Ba additions. The Ba‐containing bodies show higher permittivity values than hot‐pressed materials, while radial coupling and d33 were similar to or higher than those of the conventionally sintered pure materials.

A study of the ternary oxide LiVO 2 and its anomalous behavior

Nonstoichiometric LiVO 2 and its unusual magnetic, electrical, and thermal phase transition near 200°C were studied using X-ray diffraction, IR and EPR spectroscopy, thermoanalytical methods, and measurements of electrical resistivity and magnetic susceptibility. The transition is semireversible, appearing to be noncooperative and of higher or multiple order. It has been concluded that the driving force for the transition is not a structural instability, but rather a critical distance phenomenon involving a change in the V 3+V 3+ bond type. The low-temperature data are interpreted in terms of a two-dimensional vanadium “metal cluster layer” formed via covalent-type metal-to-metal bonds; above T t, narrow-band metallic behavior sets in within the vanadium planes. The phase transition in LiVO 2 is similar to that of TiCl 3, and is also very similar to the semiconducting-to-metallic transformations in VO 2 and V 2O 3.

Electrical properties and phase transitions of trimethylammonium-iodine-tetracyanoquinodimethane (TMA-I-TCNQ)

Temperature dependences of the resistivity and the anisotropic thermoelectric power of trimethylammonium-iodine-tetracyanoquinodimethane single crystals were measured. Two phase transitions at 150 and 82 K were confirmed by the transport measurements. Above 150 K, the transport properties are well interpreted in terms of an intrinsic semiconductor with a one-dimensional tight-binding band and a strong Coulomb interaction. The estimated band gap is 0.14 eV and the mobility ratio of electrons to holes is 0.8.

ChemInform Abstract: II. ELECTRICAL CONDUCTIVITY AND PHASE TRANSITION STUDIES ON PURE AND CADMIUM(2+)‐ OR GADOLINIUM(3+)‐DOPED POTASSIUM SODIUM SULFATES KNASO4 AND K3NA(SO4)2

Chemischer InformationsdienstVolume 14, Issue 31 Physical Inorganic Chemistry ChemInform Abstract: II. ELECTRICAL CONDUCTIVITY AND PHASE TRANSITION STUDIES ON PURE AND CADMIUM(2+)- OR GADOLINIUM(3+)-DOPED POTASSIUM SODIUM SULFATES KNASO4 AND K3NA(SO4)2 M. S. KUMARI, M. S. KUMARISearch for more papers by this authorE. A. SECCO, E. A. SECCOSearch for more papers by this author M. S. KUMARI, M. S. KUMARISearch for more papers by this authorE. A. SECCO, E. A. SECCOSearch for more papers by this author First published: August 2, 1983 https://doi.org/10.1002/chin.198331022Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume14, Issue31August 2, 1983 RelatedInformation

Electrical conductivity and phase transitions of the solid electrolyte system (Cs 1− yRb y)Cu 4Cl 3(I 2− xCl x)

Results of electrical conductivity measurements, thermal analysis, and X-ray diffraction studies indicate the existence of four phases, between 295 K and the melting points, in the system (Cs 1− y Rb y )Cu 4Cl 3I 2. These phases are designated α, á β, γ in order of decreasing temperature. The α phase is isostructural with α-RbAg 4I 5; the á phase is also cubic and very likely belongs to space group P2 13, a subgroup of P4 132 and P4 332 to which the α phase belongs. There is a high probability that the á → α transition is continuous. The á → α transition is not discernible in the conductivity measurements or thermal analysis; therefore the line of á-α transitions is presently unknown. The β phase transforms to the á and the γ phase transforms to the β phase when y ≤ 0.36; the γ phase transforms to the α phase when y ≥ 0.36. That is, there is a triple point at y = 0.36, T = 399K. The γ-β, β-α′, and γ-α transitions are all hysteretic and are therefore first order. The conductivities of the β phases are relatively low and the enthalpies of activation relatively high. The conductivity of the β phase decreases with increasing y. The β phase probably belongs to space group R3, in which the Cu + ions can be ordered. The α and á phases are the true solid electrolytes; the conductivities are high, >0.73 Ω −1cm −1 at 419 K, and the enthalpies of activation of motion of the Cu + ions low, 0.11 eV. In the system CsCu 4Cl 3(I 2−xCl x), 0 ≤ x ≤ 0.25, the Cl − for I − substitutions affect the transitions to only a small extent relative to the stoichiometric compound. The β phase occurs for all x and transforms to á.

Effect of deuteration on the electrical conductivity, dielectric constant and phase transitions in LiNH 4SO 4

Measurements of dc conductivity and dielectric constant show that deuteration causes an upward shift of the high temperature phase transition point from 186.5 to 191°C and a downward shift of the low temperature transition point from 10 to -1.5°C in LiNH 4SO 4. Mechanisms of phase transitions and of electrical transport in the crystal are discussed.

Low temperature electrical conductivity, dielectric constant, and phase transitions in (NH 4) 2SO 4 and (ND 4) 2SO 4

Careful axiswise measurements of d.c. conductivity and dielectric constants of (NH 4) 2SO 4 from 50 to - 196°C establish two distinct phase transitions, instead of one, at temperatures -49.5 and -58°C which remain unchanged in (ND 4) 2SO 4. Explanation based on successive distortions of non-equivalent (NH 4) + is offered. Low temperature transport process in the crystal also is discussed.

Effect of CdI2 on electrical conductivity and phase transition behavior in AgI

The phase transitions occurring in AgI containing dissolved CdI2 have been examined by differential thermal analysis (DTA), electrical conductivity technique, and X-ray diffractometry. The electrical conductivity and polymorphic behavior of AgI is significantly modified by low concentrations of CdI2. The results are interpreted in terms of substitutional Cd2+ and Ag+ vacancies in AgI sublattice.

Study on the electrical properties and phase transitions of lithium ferrite by a complex admittance method

The electrical properties of lithium ferrite (LiFeO 2) with rock-salt structure have been studied as a function of temperature (380–700°C) and oxygen partial pressure ( 2.1 × 10 4 −5.3 Pa) using AC conductivity measurements. Data analysis in the complex admittance plane revealed the presence of three phase transitions and mixed (electronic and ionic) conduction in LiFeO 2. The nature of the charge carriers depends on temperature and oxygen partial pressure. The defect structure of α-LiFeO 2 at high temperature has been discussed from the oxygen partial pressure dependence of electronic conductivity.

Electrical conduction and phase transitions in vacuum-deposited Cu 2− xS films

The structure, phase transitions and electrical conductivity of Cu 2− x S films deposited by vacuum evaporation at different substrate temperatures were studied. It was found that the deposition parameters significantly affect the composition and the structure of evaporated Cu 2− x S films. The stoichiometry changes from copper rich to copper deficient as the substrate temperature is increased. This is explained in terms of the mechanism of growth of the Cu 2− x S films. The occurence of phase transitions in these films was studied through measurement of the electrical conductivity as a function of temperature. Films deposited at 300 K exist in the γ phase and undergo a γ → β phase transition at 325 K and a β → α phase transition at 350 K. Films deposited at 400 K exhibit only one phase transition, the β → α transition at 345 K. A very sluggish transition from the orthorhombic to the tetragonal phase of Cu 1.96S was observed at 340 K in films deposited at 475 K. These results were corroborated by electron microscope and diffraction studies on annealed Cu 2− x S films.

Influence of crystal growth conditions on electrical properties and phase transitions in LiIO 3

D.c ionic conductivity and low frequency dielectric behaviour of α-LiIO 3 crystals grown at different pH conditions and of β-LiIO 3 crystals, are measured as a function of temperature. For α-LiIO 3 crystals, a dielectric relaxation and ionic conductivity anomaly at the α-γ phase transition are observed along the c axis. Both are very sensitive to pH growth conditions. It is proposed to explain qualitatively the α-γ transition by a mechanism similar to that of a “ionic-superionic” type transition.

Electrical Conduction and Phase Transition of Copper Sulfides

Electrical conductivity measurements have been made on copper sulfide crystals of compositions ranging from Cu1.8S to Cu2.0S and indium-doped Cu1.8S in the temperature region between 20°C and 220°C. Conductivity of Cu2-xS varied from 0.07 ohm-1cm-1 to 2400 ohm-1cm-1 as the deviation from stoichiometry increased from x=0 to x=0.2. It was found that Cu1.8S (digenite) and Cu1.96S (djurleite) undergo phase transitions at 90°C and at 93°C respectively. The transition temperature of Cu2S (chalcocite) increased from 98°C to 108°C as conductivity decreased from 52 ohm-1cm-1 to 0.07 ohm-1cm-1. An analysis of mixed conduction at β phase of low conductivity copper sulfide has shown that ionic conductivity is independent of the composition or the number of impurity cations in this material, and exhibits a temperature dependence with activation energy of 0.24 eV. Finally it is emphasized, after the discussion of the relation between electrical properties and crystal structure of copper sulfides, that the composition and crystalline phase are well characterized by the electrical conductivity in these materials.

Electrical conduction and phase transitions in CsPbCl 3

The electrical conductivity of CsPbCl 3 has been studied by d.c. and a.c. techniques in the temperature range 20–60°C. Anomalies in the conductivity are found at the phase transition at 46.2°C and at 41.9°C.

On the relation between electrical conductivity and phase transition of non-stoichiometric cuprous selenides

The electrical conductivity of non-stoichiometric cuprous selenide samples having various compositions was examined. Measurements were performed over the temperature interval where the phase transformation appears. Conductivity variations are explained considering non-stoichiometric cuprous selenide as the binary system (Cu 2Se+ Se), in which alpha and beta phases in mutual equilibrium have different compositions, i.e. different concentrations of holes. The equations derived on the basis of an equilibrium process of phase transition describe the experimental curves with satisfactory agreement. Further consequences of such an approach to non-stoichiometric compounds are also discussed.

On the relation between electrical conductivity and phase transition of non-stoichiometric cuprous selenides: Z. Ogorelec B. Čelustka Institute “Rudjer Boškovic”, Zagreb, Yugoslavia

On the relation between electrical conductivity and phase transition of non-stoichiometric cuprous selenides: Z. Ogorelec B. Čelustka Institute “Rudjer Boškovic”, Zagreb, Yugoslavia