Contains a report on a research project.National Science Foundation (Grant G-19637

Ballantyne, J. M.

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IV. FAR INFRARED SPECTROSCOPYProf. C. H. PerryJeanne H. FertelD. J. McCarthyE. C. Reifenstein IIIJ. P. Stampfel, Jr.H. D. WactlarE. F. YoungA. DIELECTRIC BEHAVIOR OF BaTiO3 SINGLE CRYSTALS IN THE INFRAREDREGIONAn investigation of the temperature and frequency dependence of the dielectric con-stant of BaTiO3 single crystals was extended to the infrared region by means of trans-mission and reflectivity measurements made with the aid of instrumentation in theSpectroscopy Laboratory, M. I. T.*300 400 500 600- 90- 80- 70Zu60- 50 ZO0- 40Z- 30- 2010700 800 900 1000 4000FREQUENCY (CM -1 )Fig. IV- 1. Infrared transmission of 3-4 thick BaTiO3 single crystal.-1lTransmission measurements in the frequency range 4000-250 cm - 1 in the infraredwere made in order to resolve the conflict between Last'sl work and the recent papersof Barker and Tinkham, 2 and Spitzer, Miller, Kleinman, and Howarth3 in the matterof lattice-vibration frequencies. Several thin crystals were prepared by Last's tech-niques and measured in transmission with Perkin-Elmer 421 and 521 double-beamspectrophotometers. The transmission curve for the best crystal, corrected forabsorptions that were due to traces of the phosphoric acid etch and for the effects ofThe work of this laboratory is supported in part by the National Science Foundation(Grant G-19637).QPR No. 73o-4100 -90-80w 70-60-50--_ -24 oC0 40- 127 °C-J - 150 0Cu, 30-w20-10-100 120 140 150 160 170 180 190 200 300 400 500 600 700 800 900 1000 4000FREQUENCY (CM- ')Fig. IV-2. Infrared reflection of single-domain BaTiO3 crystals.(IV. FAR INFRARED SPECTROSCOPY)stray radiation in the instrument, is shown in Fig. IV- 1. Contrary to Last's results,-1there is no rise in transmission in the 400-250 cm region; this shows that the secondband reported by him at 340 cm-1 is actually at the lower frequency 183 cm-1 , asfound by Spitzer et al. 3 and the present writer.The reflectivity of polarized BaTiO3 single crystals was measured in the region-1 -1 4from 1000 cm to 35 cm with the facilities described previously. 4 Samples wereprepared by etching large "butterfly" crystals in hot phosphoric acid to remove the sur-face layer, and then polarizing them to c-domain plates.5 To obtain a sufficiently largearea, two polarized crystals were butted together and then cast into an epoxy resinblock so as to maintain the plane surface.The composite reflectivity curve measured for many samples on a variety of instru-ments and at three temperatures is given in Fig. IV-2. The angle of incidence is 450from 100 cm- to Z50 cm -1, and 100 at higher frequencies. Resonances are observed-1at 491 and 182 cm-1The lattice band at 180 cm - I occurs at about the same place as that reported bySpitzer et al. 3 It has a slight temperature dependence which is easily explainable byordinary broadening with increase in temperature and by the change in lattice symmetryabove and below the Curie point. No anomalous change in the frequency or intensity ofthis band is observed as one traverses the Curie point.Accurate measurements in the submillimeter and millimeter regions indicate athird resonance at approximately 12 cm-1 which is responsible for the ferroelectricstate in BaTiO3.J. M. Ballantyne(Dr. Joseph M. Ballantyne, Research Associate in the Department of Electrical Engi-neering, has been using the equipment of our group in the Spectroscopy Laboratory,M. I. T.)References1. J. T. Last, Phys. Rev. 105, 1740 (1957).2. A. S. Barker and M. Tinkham, Phys. Rev. 125, 1529 (1962).3. W. G. Spitzer, R. C. Miller, D. A. Kleinman, and L. E. Howarth, Phys. Rev.126, 1710 (1962).4. C. H. Perry, Quarterly Progress Report No. 70, Research Laboratory of Elec-tronics, M. I. T., July 15, 1963, p. 19.5. J. M. Ballantyne, Quarterly Progress Report No. XXXII, Laboratory for Insula-tion Research, M. I. T., 1963, p. 5.6. J. M. Ballantyne, Ph. D. Thesis, Department of Electrical Engineering, M. I. T.,February 1964.QPR No. 73

Far Infrared Spectroscopy

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Far Infrared Spectroscopy

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