- Email: [email protected]
X-ray determination of the thermal expansion of calcium molybdate
2484
TECHNICAL
4. AMELINCKX S., STRUMANE G. and WEBB W. W.,J. appl. Phys.31,1359 (1960). 5. PATEL A. R. and JOHN MATHAI K., Indian J. Pure and Appl. Phys. To be published. 6. KNIPPENBERG W. F., Philips Res. Rep. 18, 161
(1963). 7. SCACE R. I. and SLACK G. A.,.I. them. Phys. 30, 1551 (1959). 8. WIEBKE G., Ber. Deut. Keram. Ges. 37,219 (1960). 9. ELMER J. H: and HOSHUBA W. J., Nepa Division Rep. No. 1770, Oak Ridge Tennessee (195 . 1),, (Unckkified). 10. SAVITSKII K. V., ILUSCHENKOV M. A., BURNAKOV K. K. and HYKONNYA A. F., Soviet Phys. Crystallogr. (English) 11,309 (1966). 11. BRACK K.,J. uppl. Phys. X5,3560 (1965).
J. Phys. Chem. Solids
Vol. 30, pp. 2484-2486.
X-ray determination of the thermal expansion of calcium molyhdate (Received 9 April 1969) INTRODUCTION IN CONNECTION with a programme of X-ray investigations, undertaken to obtain detailed information on the temperature variation of the lattice parameters, the coefficients of thermal expansion and the position and thermal parameters of the atoms in the unit cell of some Scheelite (CaWO,) type crystals, we have previously reported the results on the thermal expansion of KIO,[l] and NaIO,[2]. Results of a similar X-ray study on calcium molybdate (CaMoO,) are being presented here. EXPERIMENTAL AND RESULTS
A synthetic single crystal of CaMoO, obtained from Dr. W. S. Brower of the National Bureau of Standards, Washington, D.C. was crushed to fine powder form and filled in the specimen holder of the back
NOTES
reflection focussing Camera. X-ray powder pictures were obtained at eight different temperatures using CuK, radiation. The details of the experimental set up have been described earlier by Sirdeshmukh [3]. Unambiguous indexing of the powder lines was achieved with the help of the space group conditions and the fact that in these compounds the expansion along the c-axis is larger than that along the u-axis. Thirteen lines, (3,3, lo),,,, (604),,, (620),,,, (536),,,, (1, 1, 14),,,, (634),,,, and (44g),,, recorded in the back reflection region were used in evaluating the lattice parameters at different temperatures using Cohen’s [4] analytical method in combination with the error function, &an& Independent measurements and calculations were made on each film and the average values obtained therefrom, are given in Table 1. The standard errors calculated by the method of Jette and and Foote[5] are also tabulated. Table 1. Values of the lattice parameters of CaMoO, at different temperatures Temp. r-C)
33 75 110 158 215 265 312 355
a (A)
C (A,
5~2266~0~0001 11~4352~0~0004 5~2292~0@01 11*4420+-0.ooo4 5.2304 k 0.0002 11.4483 k 0+l005 5~2332~OXlOO2 11~4577~0*0005 5~2358&0+002 114668~0~0005 5.2385 f 0.0003 11.4769 k 0.0009 5~2415-cO~OOO2 114893r+O~O007 5*2431~O+MXll 11~4937-c0*0009
The values of the principal coefficients of expansion at different temperatures were determined by the procedure suggested by Deshpande and Mudholkar[6] and the following expressions were obtained by the usual method of statistical treatment: (Y,= 7.20 x lo++ 15.96 x lo-‘t -1.54 x lo-‘2P
TECHNICAL
2485
Table lattice
and (Yc= 11.17x 1o-g+2299x
NOTES
lo-?
2. Comparison of the parameters of CaMoO, at room temperature
+ 16.14 x lo-‘*t2. Authors
Here (Y, and (Y, are the coefficients of expansion at PC, parallel to the a and c axes respectively. The values calculated at different temperatures using the above expressions are shown in Fig. 1 along with the observed values. The mean coefficients of expansion, over the range 30”350°C, were found to be zr, = 10.13 x 10-6/“C and ac = 16.54 x lO+/“C.
;, Vegard [7] SillenandNylande@] Swanson er a[.[91 Present study
&
5.23 5.213 5.226 5.2266
11.44 11-426 11-43 1l-4352
A comparison of the principal coefficients of expansion at 30°C for a few crystals having the Scheelite structure, is made in Table 3. Table 3. Thermal expansion coeficients of a few Scheelite type crystals at 30°C Substance KIO, NaIO, CaWO, SrWO, BaWO, CdMoO, CaMoO,
51
I 90
I 160
1 240
[l 11
&X106
25.35 3%17 6.35 5-86 4.43 6.85 7.67
56-62 54.87 12.38 13.21 18.35 15.13 11-88
I 320
1.T
Fig.
111 121 [ 111 [12] [13]
a.Xl06
1. Temperature variation of the coefficients of thermal expansion of calcium molybdate.
DISCUSSION
The values of the lattice parameters of CaMoO, obtained at room temperature in the present study, are compared in Table 2 with those available in literature. There is good agreement between the values obtained in the present investigation and those reported by Swanson et a1.[93. The values of the expansion coefficients are also in good accord with those of Brower [ lo], who reports ijl, = 10.71 x 10-81”C and ac = 16.17 x lO+/“C in the range 30”-350°C as obtained by an interferometric method.
It is seen that all these crystals exhibit same type of anisotropy. For any of these compounds, the value of the thermal expansion coefficient along the tetragonal axis, is larger than that along the u-axis and remains larger at all temperatures. However in the periodates, numerical values of the expansion coefficients and the rates of their temperature variation are higher than the corresponding quantities in the tungstates and the molybdates. That the melting points of the tungstates and the molybdates are much higher than those of periodates[l4-171 is also a fact, worth a mention in this context. Structurally all these AB04 type crystals belong to the space I 4Ja of the tetragonal system. They are known to have a complex layer structure, the layers being perpendicular
2486
TECHNICAL NOTES
to the c-axis [ 181. Each layer has a two-dimensional CsCI type arrangement of An+ and BOaa- ions (n = 1 or 2). IEach ion is surrounded by eight ions of the other sign, four at the corners of a square, lying in the layers and the other four situated tetrahedrally around it. The reasoning given earlier by Deshpande ef aZ.[1,2] to explain the results of periodates, also holds good for calcium molybdate and other crystals of this group. The ionic interactions between any ion and the four ions of opposite sign lying in the same layer give rise to binding forces essentially along the layers and the interaction between this ion and the four ions of opposite sign situated at the corners of a tetr~e~on provide binding forces with components along the layers as well as in perpendicular directions. It follows from this that the binding between nei~bou~ng atoms in the layers of the lattice is stronger than that along the c-axis and so the coefficients of expansion along the u-axis can be expected to be smaller than that along the c-axis.
8. SILLEN L. G. and NYLANDER A. L., Ark. Kemi Geol. 17A, 4 (1943). 9. SWANSON H. E., GILFRICH N. T. and COOK M. I., Standard X-ray diffraction patterns, NBS Circ. No. 539,6 t 19.56). IO. BROWER W. S., Private Communi~tion (1968). 11. DESHI’ANDE V. T. and SIJRYANARAYANA S. V., Unpublishedresults. 12. DESPANDE V. T. and SURYANARAYANA S. V., J. meter. Sci. To be published( 1969). 13. DESHPANDE V. T. and SURYANARAYANA S. V., J. appl. Phys. To be publishedt 1969). 14. CHANG LUKE L. Y., SCROGER M. G. and PHILLIPS B., .I. Am. Ceram. Sot. 49, 385 (1966). 15. NASSAU K. and VAN UITERT L. G., J. appl. Phys. 31,1508 (1960). 16. BRIXNER L. H., Efectrochem. Tech. 6, 88 (1968). 17. Handbook of Chemistry and Physics (Edited by C. D. HODGMAN), pp. 545, 571. Chemical Rubber, Cleaveland, Ohio ( 1950). 18. ARBEL A. and STOKES R. J., J. appt. Phys. 36, 1460 (1965).
J. Phys. Chem. Solids
Vol. 30, pp. 2486-2490.
Coloration of LW produced by 3*0MeV @Ar ions
The authors wish to thank Dr. W. S. Brower for supplyingthem with the synthetic crystals of Calcium moly~ate used in the present inves~~tion. One of us tS.V.S.) thanks the Ministry of Education, Government of India for financialassistance.
Acknowtegemenrs-
V. T. DESHPANDE S. V. SURYANA~YANA Physics Department, C&mania University, Hyderabad-7, India REFERENCES 1. DESHPANDE V. T., PAWAR R. R. and SURYANARAYANA S. V., Crtrr. Sci. 36, 513 f 1967). S. V. 2. DESHPANDE V. T., SURYANA~YANA and PAWAR R. R., Acta crystallogr. A24, 398 ( 1968). 3. SIRDESHMUKH D. B., Ph.D. Thesis. Osmania University ( 1963). 4. COHEN M. U., Reu. scient. Instrum. 6,68 11935). 5. JETI’E E. R. and FOOTE F., J. them. Phys. 3,605 (1935). 6. DESHPANDE V. T. and MUDHOLKAR V. M., 1nd.J. Phys. 35,434 (1961). 7. VEGARD L., Skr. Norske Vid. Akad. Oslo nr 11 (1925).
~Rece~ved 28 March 1969) EXTENSIVE
studies have established that the exposure of alkali halide crystals to ionizing radiation results in the production of color center bands. These studies have been restricted for the most part to irradiations by U.V. rays, X-rays, gamma rays, electrons, protons and neutrons. Little isolation has been reported, however, as to the color center bands produced by energetic massive ions, Since the penetration depth of the massive ions is quite small it is possible to investigate color center, e.g. the F-center, concentrations in crystals which are otherwise too opaque for ordinary optical measurements. LiF was used in this investigation since preliminary coloration studies with various alkali halides exposed to energetic argon ions indicated that the damage was quite stable in LiF at room temperature. The dominant color
TECHNICAL
4. AMELINCKX S., STRUMANE G. and WEBB W. W.,J. appl. Phys.31,1359 (1960). 5. PATEL A. R. and JOHN MATHAI K., Indian J. Pure and Appl. Phys. To be published. 6. KNIPPENBERG W. F., Philips Res. Rep. 18, 161
(1963). 7. SCACE R. I. and SLACK G. A.,.I. them. Phys. 30, 1551 (1959). 8. WIEBKE G., Ber. Deut. Keram. Ges. 37,219 (1960). 9. ELMER J. H: and HOSHUBA W. J., Nepa Division Rep. No. 1770, Oak Ridge Tennessee (195 . 1),, (Unckkified). 10. SAVITSKII K. V., ILUSCHENKOV M. A., BURNAKOV K. K. and HYKONNYA A. F., Soviet Phys. Crystallogr. (English) 11,309 (1966). 11. BRACK K.,J. uppl. Phys. X5,3560 (1965).
J. Phys. Chem. Solids
Vol. 30, pp. 2484-2486.
X-ray determination of the thermal expansion of calcium molyhdate (Received 9 April 1969) INTRODUCTION IN CONNECTION with a programme of X-ray investigations, undertaken to obtain detailed information on the temperature variation of the lattice parameters, the coefficients of thermal expansion and the position and thermal parameters of the atoms in the unit cell of some Scheelite (CaWO,) type crystals, we have previously reported the results on the thermal expansion of KIO,[l] and NaIO,[2]. Results of a similar X-ray study on calcium molybdate (CaMoO,) are being presented here. EXPERIMENTAL AND RESULTS
A synthetic single crystal of CaMoO, obtained from Dr. W. S. Brower of the National Bureau of Standards, Washington, D.C. was crushed to fine powder form and filled in the specimen holder of the back
NOTES
reflection focussing Camera. X-ray powder pictures were obtained at eight different temperatures using CuK, radiation. The details of the experimental set up have been described earlier by Sirdeshmukh [3]. Unambiguous indexing of the powder lines was achieved with the help of the space group conditions and the fact that in these compounds the expansion along the c-axis is larger than that along the u-axis. Thirteen lines, (3,3, lo),,,, (604),,, (620),,,, (536),,,, (1, 1, 14),,,, (634),,,, and (44g),,, recorded in the back reflection region were used in evaluating the lattice parameters at different temperatures using Cohen’s [4] analytical method in combination with the error function, &an& Independent measurements and calculations were made on each film and the average values obtained therefrom, are given in Table 1. The standard errors calculated by the method of Jette and and Foote[5] are also tabulated. Table 1. Values of the lattice parameters of CaMoO, at different temperatures Temp. r-C)
33 75 110 158 215 265 312 355
a (A)
C (A,
5~2266~0~0001 11~4352~0~0004 5~2292~0@01 11*4420+-0.ooo4 5.2304 k 0.0002 11.4483 k 0+l005 5~2332~OXlOO2 11~4577~0*0005 5~2358&0+002 114668~0~0005 5.2385 f 0.0003 11.4769 k 0.0009 5~2415-cO~OOO2 114893r+O~O007 5*2431~O+MXll 11~4937-c0*0009
The values of the principal coefficients of expansion at different temperatures were determined by the procedure suggested by Deshpande and Mudholkar[6] and the following expressions were obtained by the usual method of statistical treatment: (Y,= 7.20 x lo++ 15.96 x lo-‘t -1.54 x lo-‘2P
TECHNICAL
2485
Table lattice
and (Yc= 11.17x 1o-g+2299x
NOTES
lo-?
2. Comparison of the parameters of CaMoO, at room temperature
+ 16.14 x lo-‘*t2. Authors
Here (Y, and (Y, are the coefficients of expansion at PC, parallel to the a and c axes respectively. The values calculated at different temperatures using the above expressions are shown in Fig. 1 along with the observed values. The mean coefficients of expansion, over the range 30”350°C, were found to be zr, = 10.13 x 10-6/“C and ac = 16.54 x lO+/“C.
;, Vegard [7] SillenandNylande@] Swanson er a[.[91 Present study
&
5.23 5.213 5.226 5.2266
11.44 11-426 11-43 1l-4352
A comparison of the principal coefficients of expansion at 30°C for a few crystals having the Scheelite structure, is made in Table 3. Table 3. Thermal expansion coeficients of a few Scheelite type crystals at 30°C Substance KIO, NaIO, CaWO, SrWO, BaWO, CdMoO, CaMoO,
51
I 90
I 160
1 240
[l 11
&X106
25.35 3%17 6.35 5-86 4.43 6.85 7.67
56-62 54.87 12.38 13.21 18.35 15.13 11-88
I 320
1.T
Fig.
111 121 [ 111 [12] [13]
a.Xl06
1. Temperature variation of the coefficients of thermal expansion of calcium molybdate.
DISCUSSION
The values of the lattice parameters of CaMoO, obtained at room temperature in the present study, are compared in Table 2 with those available in literature. There is good agreement between the values obtained in the present investigation and those reported by Swanson et a1.[93. The values of the expansion coefficients are also in good accord with those of Brower [ lo], who reports ijl, = 10.71 x 10-81”C and ac = 16.17 x lO+/“C in the range 30”-350°C as obtained by an interferometric method.
It is seen that all these crystals exhibit same type of anisotropy. For any of these compounds, the value of the thermal expansion coefficient along the tetragonal axis, is larger than that along the u-axis and remains larger at all temperatures. However in the periodates, numerical values of the expansion coefficients and the rates of their temperature variation are higher than the corresponding quantities in the tungstates and the molybdates. That the melting points of the tungstates and the molybdates are much higher than those of periodates[l4-171 is also a fact, worth a mention in this context. Structurally all these AB04 type crystals belong to the space I 4Ja of the tetragonal system. They are known to have a complex layer structure, the layers being perpendicular
2486
TECHNICAL NOTES
to the c-axis [ 181. Each layer has a two-dimensional CsCI type arrangement of An+ and BOaa- ions (n = 1 or 2). IEach ion is surrounded by eight ions of the other sign, four at the corners of a square, lying in the layers and the other four situated tetrahedrally around it. The reasoning given earlier by Deshpande ef aZ.[1,2] to explain the results of periodates, also holds good for calcium molybdate and other crystals of this group. The ionic interactions between any ion and the four ions of opposite sign lying in the same layer give rise to binding forces essentially along the layers and the interaction between this ion and the four ions of opposite sign situated at the corners of a tetr~e~on provide binding forces with components along the layers as well as in perpendicular directions. It follows from this that the binding between nei~bou~ng atoms in the layers of the lattice is stronger than that along the c-axis and so the coefficients of expansion along the u-axis can be expected to be smaller than that along the c-axis.
8. SILLEN L. G. and NYLANDER A. L., Ark. Kemi Geol. 17A, 4 (1943). 9. SWANSON H. E., GILFRICH N. T. and COOK M. I., Standard X-ray diffraction patterns, NBS Circ. No. 539,6 t 19.56). IO. BROWER W. S., Private Communi~tion (1968). 11. DESHI’ANDE V. T. and SIJRYANARAYANA S. V., Unpublishedresults. 12. DESPANDE V. T. and SURYANARAYANA S. V., J. meter. Sci. To be published( 1969). 13. DESHPANDE V. T. and SURYANARAYANA S. V., J. appl. Phys. To be publishedt 1969). 14. CHANG LUKE L. Y., SCROGER M. G. and PHILLIPS B., .I. Am. Ceram. Sot. 49, 385 (1966). 15. NASSAU K. and VAN UITERT L. G., J. appl. Phys. 31,1508 (1960). 16. BRIXNER L. H., Efectrochem. Tech. 6, 88 (1968). 17. Handbook of Chemistry and Physics (Edited by C. D. HODGMAN), pp. 545, 571. Chemical Rubber, Cleaveland, Ohio ( 1950). 18. ARBEL A. and STOKES R. J., J. appt. Phys. 36, 1460 (1965).
J. Phys. Chem. Solids
Vol. 30, pp. 2486-2490.
Coloration of LW produced by 3*0MeV @Ar ions
The authors wish to thank Dr. W. S. Brower for supplyingthem with the synthetic crystals of Calcium moly~ate used in the present inves~~tion. One of us tS.V.S.) thanks the Ministry of Education, Government of India for financialassistance.
Acknowtegemenrs-
V. T. DESHPANDE S. V. SURYANA~YANA Physics Department, C&mania University, Hyderabad-7, India REFERENCES 1. DESHPANDE V. T., PAWAR R. R. and SURYANARAYANA S. V., Crtrr. Sci. 36, 513 f 1967). S. V. 2. DESHPANDE V. T., SURYANA~YANA and PAWAR R. R., Acta crystallogr. A24, 398 ( 1968). 3. SIRDESHMUKH D. B., Ph.D. Thesis. Osmania University ( 1963). 4. COHEN M. U., Reu. scient. Instrum. 6,68 11935). 5. JETI’E E. R. and FOOTE F., J. them. Phys. 3,605 (1935). 6. DESHPANDE V. T. and MUDHOLKAR V. M., 1nd.J. Phys. 35,434 (1961). 7. VEGARD L., Skr. Norske Vid. Akad. Oslo nr 11 (1925).
~Rece~ved 28 March 1969) EXTENSIVE
studies have established that the exposure of alkali halide crystals to ionizing radiation results in the production of color center bands. These studies have been restricted for the most part to irradiations by U.V. rays, X-rays, gamma rays, electrons, protons and neutrons. Little isolation has been reported, however, as to the color center bands produced by energetic massive ions, Since the penetration depth of the massive ions is quite small it is possible to investigate color center, e.g. the F-center, concentrations in crystals which are otherwise too opaque for ordinary optical measurements. LiF was used in this investigation since preliminary coloration studies with various alkali halides exposed to energetic argon ions indicated that the damage was quite stable in LiF at room temperature. The dominant color