摘要:

The electrical conductivity &sgr;, thermoelectric powerQ, and Hall coefficientRare examined as a function of the ratio of hole‐to‐electron concentrationsp/nfor a nondegenerate semiconductorat constant temperature. From these relations the fundamental parameters of the material (forbidden band gap, mobilities, and effective masses) can be derived. This approach is particularly applicable to materials whose stoichiometry varies as a function of temperature and vapor pressure of the constituentsP. For any model of this equilibrium decomposition, it is easy to transform the calculations in terms ofp/ninto results as a function ofP. Asp/nincreases, &sgr; passes through a minimum, whileQandRtraverse minimum (negative), zero, and maximum (positive) values. These extrema are of special interest. In the simple case of one kind of imperfection, &sgr;,Q, andRbecome independent ofPin a certain pressure range (i.e., when the intrinsic conditionn=phas been reached). It is then possible to derive the ratio of mobilities &mgr;n/&mgr;pand the ratio of the average effective massesmn*/mp* from &sgr;(P) andQ(P) only. Hence, if &mgr;normn* are known (i.e., from measurements at lower temperatures), one can calculate these parameters for the other charge carrier.

ISSN:0021-8979    

DOI:10.1063/1.1777139

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

Mixed crystals of potassium chloride and bromide show strong internal strain evidenced by cracking. The minimum of the melting point occurs between 63 and 65 mole % KBr. The microhardness between 25 and 65 mole % KBr is more than twice that of either component. The lattice constant changes linearly with composition. The macrodensity deviates by several percent, indicating a high concentration of defects. The intensity of coloration by electrons shows that defects are not mainly due to vacancies but presumably to larger aggregates of submicroscopic size or interstitials. The broadening of exciton bands, as measured by shifts of the ultraviolet absorption edge, is greatest at a 2:1 KCl&sngbnd;KBr ratio. This may indicate a certain short‐range order in KCl&sngbnd;KBr mixed crystals.

ISSN:0021-8979    

DOI:10.1063/1.1777140

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

Detailed electron microscope observations of plastically deformed and annealed magnesium oxide have been made. After cold work the material contains trails of elongated prismatic dislocation loops, of which the majority corresponds to a sheet of interstitial ions. On annealing at temperatures between 850° and 1600°C these trails break up into circular loops of edge dislocation and the loops then increase in size. The process occurs by the motion of vacant lattice sites along dislocation lines and possibly through the bulk material. The kinetics of the former process is described. A theory of breakup by pipe diffusion has been developed and used to obtain an activation energy for the motion of point defects in the core of a dislocation of ∼3.1 ev.

ISSN:0021-8979    

DOI:10.1063/1.1777141

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

On the basis of the electron theory of chemisorption, a criterion is deduced for the positive and negative photoadsorptive effect on semiconductors (photoadsorption and photodesorption). A relation is established between the sign of the effect and the nature of the adsorbent and adsorbate, the previous treatment of the sample, and the experimental conditions (temperature and pressure). The available experimental material is analyzed and interpreted from the standpoint of the proposed theory.

ISSN:0021-8979    

DOI:10.1063/1.1777142

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

The wide diversity of studies carried out on transport phenomena in AgBr permits a critical evaluation of the success and failures of existing theories of ion kinetics and defect equilibrium. Some unsolved problems relating to polarization, microwave dielectric constant, creep, thermoelectric power, and their relation to mobility and density of defects are discussed.

ISSN:0021-8979    

DOI:10.1063/1.1777143

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

Recent experiments on the dc ionic conductivity of NaCl crystals doped with divalent cation impurities led to a re‐evaluation of some of the basic constants for defect formation and motion in these crystals. The key parameter is the energy of motion &egr;mof a cation vacancy. This parameter has been determined from the temperature dependence of the conductivity under conditions where the concentration of cation vacancies remains fixed. Such conditions apply (1) in the range just below the intrinsic region, and (2) in samples rapidly cooled to below 0°C such as to prevent the attainment of an equilibrium degree of association. From the present work combined with previous data, the jump rate of the isolated positive‐ion vacancy in NaCl is &ngr;=12&ngr;0exp(−&egr;m/kT) with &ngr;0=1014.1±0.3sec−1and &egr;m=0.80±0.02 ev. With the aid of earlier measurements in the intrinsic range it is concluded that the energy of formation of a Schottky defect in an NaCl crystal is 2.12±0.06 ev, while the entropy of formation is 6.2±1.8 (in units ofk). Very similar results, although of somewhat lower precision, apply to KCl. Finally, a comparison is made between these values and the predictions of existing theories.

ISSN:0021-8979    

DOI:10.1063/1.1777144

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

Pure silver chloride crystals, when cooled rapidly from high temperatures, show enhanced ionic conductivity which may be attributed to quenched‐in Schottky defects. From the annealing out of this extra conductivity one deduces that for an associated vacancy pair the binding energy is 0.42 ev and the migration energy is ≥1.0 ev. The decorability of interior dislocations by swept‐in photoelectrons is also discussed and is shown to be sensitive to the purity of the crystal.

ISSN:0021-8979    

DOI:10.1063/1.1777145

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

Ionic conductivity in the extrinsic range of temperature (250° to 400°C) was measured for specimens taken from a single‐crystalline ingot of KCl subjected to zone purification. The effect of dislocation density was studied in order to clarify the nature of ionic conduction in these highly purified crystals. Conductivity increased by a factor of 10 in the purest crystals by increasing dislocation density from 106to 107cm−2. Conductivity was decreased in the impurer crystals by increasing the density of dislocations. Comparing the results with predictions from charged dislocation theory, the value of 0.7 ev is obtained for the formation energy of positive ion vacancies.

ISSN:0021-8979    

DOI:10.1063/1.1777146

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

Oxygen‐18 exchange between gaseous oxygen and cadmium oxide crystals has been studied in the temperature range 630° to 855°C. Since isotope equilibrium is not instantaneously established at the crystal surface an appropriate solution for this particular diffusion problem has been given. In this way it is possible to evaluate rate constants (K) of the phase boundary reaction as well as lattice diffusion constants (D):D=3.8·106exp(−92±4/RT);  K=1.3·102exp(−49±11/RT).The influence of the ambient oxygen pressure (D∼po2−1/5) indicates that a vacancy mechanism is operative in the diffusion of oxygen. This is substantiated by the finding that diffusion is enhanced by incorporation of Li2O. From experiments with doped crystals the fraction of vacancies can be estimated, e.g., 4.4·10−4in ``pure'' CdO at 790°C and 0.16 atm O2. On the basis of thermodynamic considerations the energy of formation of defects can be estimated at 29 leaving 63 kcal/mole for the activation energy of the diffusion process proper.The rate constant of the phase boundary reaction increases with decreasing oxygen pressure (K∼po2−⅓) as well as with increasing Li2O addition. These findings offer a possibility for the suggestion of a mechanism of the surface exchange process.

ISSN:0021-8979    

DOI:10.1063/1.1777147

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

Observations of the motion of ions by means of both diffusion and electrical conductivity measurements usually show deviations from the normal Einstein relation. The interpretation of these deviations often leads to a fairly detailed picture of the types of defects present and the mechanisms of their motion. A correction must always be considered because of the fact that successive jumps of a tracer atom are correlated, as first discussed by Bardeen and Herring, and the origin of this effect is shown by treating diffusion as a random walk problem. For the interstitialcy mechanism a second correction is required because the effective displacement is larger for conductivity than diffusion, and this effect is illustrated with results on AgCl and AgBr. Possible mechanisms for ionic motion in crystals with the CsCl structure are described, and the present interpretation of results for CsBr, CsI, and TlCl is discussed. It appears that vacancy pairs may make an appreciable contribution to the diffusion. Experiments for observing diffusion with an applied electric field are discussed, and an analysis is given of the problem of determining the internal electric field in such situations. If certain experimental difficulties can be overcome, this last technique should provide a powerful extension of methods of investigating the motion of ions in crystals.

ISSN:0021-8979    

DOI:10.1063/1.1777148

出版商:AIP    

年代:1962

数据来源: AIP