TEMPERATURE AND PRESSURE DEPENDENCES OF ELASTIC CONSTANTS IN MERCURY-TELLURIDE CONTAINING 3 AND 20 PERCENT MANGANESE FROM ULTRASONIC-VELOCITY MEASUREMENTS
Abstract
Measurements have been made of the transit times of 30 MHZ longitudinal and transverse ultrasonic waves in Hg(,0.97)Mn(,0.03)Te and Hg(,0.8)Mn(,0.2)Te as functions of the temperature from 1.5 to 298 K and of hydrostatic pressure P up to 2.5 kbar. Second order elastic constants obtained therefrom are C(,L) = (C(,11) + C(,12) + 2C(,44)) / 2, C(,S) = (C(,11) - C(,12)) / 2 and C(,44). While the temperature dependences of the elastic constants of HgTe and Hg(,0.97)Mn(,0.03)Te are very similar, those of Hg(,0.8)Mn(,0.2)Te are significantly smaller. The temperature dependences of elastic constants can be fitted by Lakkad's anharmonic model. Below 200 K the explicitly temperature dependent term is more important than the thermal expansion term. From the elastic constants at 1.5 K the elastic Debye temperatures are deduced to be 143.2 (+OR-) 0.4 K for Hg(,0.97)Mn(,0.03)Te and 144.1 (+OR-) 0.9 K for Hg(,0.8)Mn(,0.2)Te respectively. In Hg(,1-x)Mn(,x)Te samples the values of (PAR-DIFF)C(,L)/(PAR-DIFF)P are about equal, the values of (PAR-DIFF)C(,S)/(PAR-DIFF)P and (PAR-DIFF)C(,44)/(PAR-DIFF)P decrease with increasing x except that (PAR-DIFF)C(,S)/(PAR-DIFF)P is equal in HgTe and Hg(,0.97)Mn(,0.03)Te. The second order elastic constants at 298 K are used to deduce the harmonic force constants and Phillips ionicity for the Hg(,1-x)Mn(,x)Te samples with x > 0. The presence of 3d electrons on Mn makes the bond-bending force constants smaller in Hg(,1-x)Mn(,x)Te for larger x. From application of Bienenstock and Burley's model of structure and bonding, it is found that for a number of III-V and II-VI compounds, (gamma)(,C(,11)) is independent of ionicity, but (gamma)(,C(,S)) (except for HgTe and Hg(,0.97)Mn(,0.03)Te) and (gamma)(,C(,44)) (except for GaP, GaAs and GaSb) increase with decreasing ionicity. Use of modified Born criterion of Demarest et al., and the elastic constants data up to 2.5 kbar structural transition pressures P(,t) are deduced to be 12.6 and 10 kbar for Hg(,0.97)Mn(,0.03)Te and Hg(,0.8)Mn(,0.2)Te, respectively, at room temperature. The Phillips' relation for correlating ionicity with the change in Gibbs free energy at P(,t) is satisfied by Hg(,1-x)Mn(,x)Te samples which have lower P(,t) and higher ionicity for larger x. For the Hg(,1-x)Mn(,x)Te samples, present models are adequate for obtaining three of the third order elastic constants and one of the anharmonic force constants but not for determining the remaining three of the third order and two of the anharmonic force constants from the pressure dependences data of elastic constants.
Degree
Ph.D.
Subject Area
Condensation
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