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Crystal structures and lattice parameters of the compounds of berkelium—IV berkelium trifluoride
J. inorg,nucl.Chem.,1968,Vol.30,pp. 1775to 1784. PergamonPress. Printedin Great Britain
CRYSTAL STRUCTURES AND LATTICE PARAMETERS OF THE COMPOUNDS OF B E R K E L I U M - IV BERKELIUM TRIFLUORIDE* J. R. P E T E R S O N t and B. B, C U N N I N G H A M Department of Chemistry and Lawrence Radiation Laboratory, University of California, Berkeley, California ( R e c e i v e d 1 D e c e m b e r 1967)
Abstract-BkF:~ has been found to exhibit a low-temperature, YFa-type orthorhombic structure and a high-temperature, LaF3-type trigonal structure. The lattice parameters of these two BkF:~ modifications are: a0 = 6"70-+0'01 A, bo = 7"09+-0"01 A, co = 4.41 +_0.01,4 (orthorhombic), and a0 = 6.97_+0.01A, c0=7.14_+0.01A (trigonal), where the error limits reflect the uncertainties in the derivation of the lattice parameters. The inversion temperature of BkF3 lies in the range 350 to 600°C. INTRODUCTION
TUE PREPARATION and crystallographic characterization of two structural forms
of berkelium trifluoride are described in this paper. EXPERIMENTAL The berkelium used in this work was derived from two separate purification cycles, both carried out as described previously[l]. Mass analyses of the two berkelium solutions showed the Ce and Nd contents to be 0.27 atom per cent Ce and 0.06 atom per cent Nd in one Bk solution, as contrasted with 9-53 atom per cent Ce and 0.03 atom per cent Nd in the other. The difference is attributed to the failure of the alcoholic HCI column, used to separate Bk and Ce, in the second purification cycle. The presence of the cerium and californium (from decay of 249Bk at a rate of - 0-2 per cent per day) contaminants prevented the determination of accurate lattice parameters for BkFa. Berkelium trifluoride samples were prepared by treatment of the oxides (stuck on a 5-rail Pt wire inside a hole in a ~-in Pt rod) with a one-to-two H2cgrHF~g) mixture at 600°C for ½hr, followed by a second, similar treatment with a fresh H2~grHFig) mixture. The trifluoride samples were either cooled rapidly to obtain the high-temperature, LaFa-type trigonal modification, or cooled slowly to obtain the low-temperature, YF~-type orthorhombic modification. In both cases the samples were cooled in the reaction gas mixture and then flushed with argon gas before removal from the all-Monel vacuum system. The very pale yellow-green trifluoride samples were "chipped off" the Pt wire into a quartz capillary, which was subsequently evacuated and sealed off for X-ray examination. Further details of the hydrofluorination techniques can be found in Ref. [2]. X-ray exposure times, using the same diffraction equipment and operating conditions as reported for the oxide work[l], were from eight to twelve hr on the 0.2/~g BkFa samples. *The experimental work reported here is taken from a thesis submitted by J. R. Peterson to the Graduate Division of the University of California in partial fulfillment of the requirements for the degree of Doctor of Philosophy. tPresent address: Department of Chemistry, The University of Tennessee, Knoxville, Tennessee 37916. 1. J. R. Peterson and B. B. Cunningham, inorg, nuel. Chem. Left. 3, 327 (1967). 2. J. R. Peterson, (Ph.D. Thesis), University of California Lawrence Radiation Laboratory Report, UCRL-17875 (October 1967). 1775
1776
J.R.
PETERSON RESULTS
a n d B. B. C U N N I N G H A M AND
DISCUSSION
Berkelium trifluoride was found to exist in both the LaF3-type trigonal structure[3], characteristic of the lanthanide trifluorides of La through Pro, and the YF3-type orthorhombic structure[4], characteristic of the lanthanide trifluorides of Sm through Lu. All of the BkF3 powder patterns showed the presence of more than one phase. Usually all the lines were accounted for by a trigonal trifluoride phase plus an orthorhombic trifluoride phase, but in some cases other, unaccounted-for lines were present in the powder patterns. One phase was always dominant, however, and only the more intense lines of the other phases were observed. Because of the possible superposition of lines belonging to different trifluoride phases, the observed line intensities for each separate phase are subject to error. In one case (JP-VII, Film 2691A) enough of the minor YF~-type orthorhombic phase was observed to determine lattice parameters for it. The observed lattice parameters of the individual trifluoride preparations along with their 24aCf and Ce contents are listed in Table I. Since CeF3 does not exhibit an orthorhombic modification, the YF3-type berkelium trifluoride lattice parameters were initially corrected for the known Cf content of the Bk sample in accordance with Vegard's Law[5]. The lattice parameters of orthorhombic CfFa (ao = 6-653 ± 0.002 A, b0 = 7.041 ___0.002 A, and Co = 4.395 __+0.001 A) were derived from a single preparation by Peterson et al. [6]. These "corrected-forCf", orthorhombic BkFa lattice parameters were then plotted vs. the Ce content of the berkelium sample and extrapolated to zero Ce content to obtain "best Table 1. Berkelium trifluoride lattice parameters
Sample number
Film number
Structure type
z49Cf* content (atom %)
Total Cet content (atom %)
Observed lattice parameters~; (,4) a0 -+ 2o-
JRP-XXIII JP-VII JP-X JRP-XXI JRP-XXII JP-VII JP-X JP-X
2624A 2691A 2713A 2614A 2619A 2691A 2716A 2734A
YFa YF a YF~ LaF3 LaFa LaFa LaFa LaFs
7-03 1.53 5-16 5.26 6-20 1-53 5.79 8-05
0.27 9.53 9.53 0.27 0.27 9.53 9.53 9.53
6.695-4-0.004 6.717-+0.015 6.716-+0.001 6.973-+0.002 6.965-+0.003 6-990-+0.001 6.990±0.001 6.988-+0.001
bo -+ 2 o-
c0-+ 2Gr
7.086--_0-004 4.407-+0.003 7.114-----0.011 4.409-+0.005§ 7-103 -+0.001 4.408-+0.001 7-143 ~0.003 7.140±0.003 7.157-+0.001 7.158---0.002 7.156±0.002
*Calculated assuming 24*Bkhalf-life is 314 days. tDetermined by mass analysis. See text. :[:Lattice parameters are the least squares value. The 2 o- error limits represent the 95 per cent confidence range reflecting only the internal consistency of the data for the individual preparation. §The second phase in a predominantly trigonal BkFa powder pattern.
3. Allan Zalkin, D a v i d H. Templeton, and T e d E. Hopkins, lnorg. Chem. 5, 1466 (I966). 4. Allan Zalkin and D. H. Templeton, J.Am. chem. Soc. 75, 2453 (1953). 5. A. F. Wells, Structural Inorganic Chemistry, Chapter X X V I I , pp. 9 7 1 - 1 0 2 8 . Oxford University Press, London (1962). 6. J. R. Peterson, J. C. Copeland, and D. Temple, University of California Lawrence Radiation Laboratory, Unpublished results (1967).
Crystal structures and lattice parameters of the compounds of berkelium - IV
1777
estimates" for the lattice parameters of orthorhombic BkF3:a0 = 6.70___ 0.01 A, b0 = 7.09+__0.01A, and co = 4.41--4-_0.01A, where the error limits reflect the uncertainties in the derivation of the lattice parameters. Similarly for LaF3-type trigonal berkelium trifluoride, since the trigonal modification of CfF3 is unknown, the lattice parameters were corrected for the known Ce content of the Bk sample using the parameters of Swanson et al. (a0 = 7.112A and co = 7.279A)[7]. These "corrected-for-Ce," trigonal BkF:~ lattice parameters did not vary in any regular fashion as the Cf content of the berkelium sample increased, so they were just averaged to obtain "best estimates" for the lattice parameters of trigonal BkF3: a0 = 6 . 9 7 _ 0.01 A and Co = 7- 14___ 0.01 A, where again the lattice parameters are rounded off to the nearest hundredth and the error limits reflect the uncertainties in the derivation of the lattice parameters. The Miller indices, observed and calculated 2 0 values, and observed and calculated line intensities for one sample of each type of BkF:~ are given in Tables 2 and 3. Table 2. Line list and indexing for YF3-type orthorhombic BkF3 (J P-X, Film 2713A) 20 (deg)
Line intensity
Observed*
Calculatedt
Observed*
Calculated~
011 101 020 200 111 210 201 121 211 002 221
23.67 24.12 25"02 26-47 27.27 29.37 33.51 35.06 35.90 40-85 42.25
23.75 24.15 25.07 26.54 27.26 29.42 33-55 35.09 35.91 40.94 42.34
6.5 9.0 9.0 1.5 10.0 10.0 3.5 9.0 3.0 6.5 6-5
2.0 5-7 6.3 0.1 10.0 7,6 0.4 3.1 0.1 1.1 1-4
102~ 03 I J 112
43.14
43.20 43-38 45.13
4.0
~0-4 t0' 1 1.8
301 ~ 131/ 230 311 022 122
45.44
45.44 45-53 46.95 47.30 48-61 50-60
10.0
212/ 0401 321 400 141
51.23
hkI
44.99
46.84 47.29 48.54 50.53
52"58 54"53 57-57
51.21 51"46 52-59 54'66 57-62
6.5
8.5 7-0 7.0 7.0 8.0 broad 7"5 5"5 6'0
~2-4 (3.6 3.2 1.8 1.5 1.4 {2.3 1"2 2"1 0"9 1-0
7. H. E. Swanson, N. T. Gilfrich, M. I. Cook, R. Stinchfield and P. C. Parks, National Bureau of Standards Circular No. 539, Vol, 8. U.S. Government Printing Office, Washington, D.C. (1959); AS T M X-RA Y Diffraction Card No. 8-45.
J. R. PETERSON and B. B. CUNNINGHAM
1778
Table 2. (Contd.)
20 (deg)
Line intensity
hkl
Observed*
Calculatedt
Observed*
Calculated$
302~ 132J 312/. 411[ 331J 420 241 232 013~ 322J 113 042 430 142~ 051J
58.82
5.8
88.28
58.79 58.87 60.35 60.42 60.68 61.04 62.84 64.03 64.78 64.91 66.44 67.76 68.51 69.38 69.52 69.87 70-50 70"79 71 '05 71"12 72"17 72"20 72'23 75'13 75"52 76" 14 76"26 78"38 79"29 81 "26 81"88 81.95 83'52 86.10 86.30 86.50 88.40
3.5 broad
{0.2 0.6 {0.7 0.4 0.9 1.0 0.3 1.1 {0.8 0.3 0.3 0.5 0-1 {0.4 0.1 0.6 0.4 {0'2 1"0 0"7 {0"2 0"6 0.2 0-8 1'2 ~0"8 10"4 0"6 0'3 0.4 {0"2 0"3 0"4 {0"7 0.4 0.6 0.5
413~ 522J
89.73
89.75 89.86
5-5 broad
{0.8 0.4
114~
91-78
91.63 91-88
5.0
352~ 45 lJ 062t 541 124J 532~ 162J
93.96
94.05 94.11 95.32 95.56 95.69 96.63 96.84
203 402 123]. 341~ 151J 332// 250} 431J 511 223 422~ 033J 440 521 060 342~ 152J 351 5311 161~ 252.1 610
243.1
60.37 61.02 62.77 64.01 64.76 66-31 67.65 68.45 69.35 69.80 70.40 71"05 72' 15 75"10 75"45 76"15 78-39 79' 19 81.23 81 "83 83"63 86-23
95-51 96.81
7.5 6.5 3.5 6-5 6-5 3.0 4.5 1.5 3.0 3.0 2.5 7"0 5"5 4'0 6"0 5"0 3'5 3.0 4"3 4"0 3-0 6.5 broad
3.5 broad 4.5 broad 1"5 broad
{0.4
0.7
{0.3 0.2 {0.2 0.2 0.4 {0.1 0.2
Crystal structures and lattice parameters of the compounds of berkelium- I V Table 2. (Contd.)
20 (deg) hkI
Observed*
053] 361J 630] 343~ 153J 433 ~l 304 c~] 612 c~l~ 134 ~lJ 314~1] 171 c~1~ 270 ~1 460 c~1 542 c~1 542 c~2 551 ~1"~ 324a~J 551 ~ ] 324 c~2J 362 c~l 701 c~1 711 oq'~ 144 c~iJ 632al 533 cq| 172a1[ 334 c~d 721 cq 371 721 ~e 263 oq] 272 cq~ 1)80 c~1 462 c~1 650 ~1 712 a ~ 453 ~1) 712 ~" 561 cq 453 c~ 344 623 154 c~ 181 c~ 344 a2 623 ~z 154 c~z 181 c~
al} l
98"26 99"36 100-51 102.36
103"91 104.95 105-50 106-09 106.59 107.84 108.29 109-09 110"54 112-29 113-79 115.04 116.39 116-78
Line intensity
Calculatedt 98.01 98.42 99-24 99.47 99.54 100.49 102-34 102.40 102.41 103.72 103.87 104-93 105.52 106-15 106.53 107.86 107.92 108.25 108.31 109.12 111).49 I 11.94 112.30 113.76 114.76 115.02 115.17 116.37
Observed*
4.0 2.5 broad 3.5 4-0
3-5 2-0 I-8 1.3
2.0 1-0 broad 2.0
2.0 3.5 3.0
126.20 126.24 126.34 126.72
5.8
126.82
126.76 126.80 126.90
3-0
124.52
0'1 0"2
3.0 broad
126.22
123.92
0"3 0'3 0'2 0'1
4.0
2.3
120-72 122.27
0-4 0.1 0-1 0"4 0-1 0-3 0"3
4-0
I 16.76 116.83 120.09 120.12 120.34 120.78 122-34 123.83 123.94 124.37 124-43 124.48 126.15
120.13
Calculatedt
5-5 3.0 1.8 5.0 3-0
0.3 O.I
t0:I
0.4
0.5 0.3 0.1 0.3 0-3 0.3 0.5 0.1 0.1 0.3 0-2 0-4 0.3 0-2 0.1 0.2 0.1 0.1
1779
1780
J. R. P E T E R S O N and B. B. C U N N I N G H A M Table 2. (Contd.)
20 (deg) h kI 205 al 1 372 a l l 471 a l l 504 a l l 205 a2] 372 a2[ 471 ot2[ 504 ~sJ 281 c~l 281 a2 800 a 073 a 810 oq 633 al 073 a2 225 cq" 741 cq 173 al 524 oqj 225 a2 ] 741 a2[ 173 a,~ 524 a 2 | 035 a l J 732 cq ] 035 as [ 562a1[ 082alJ 182 a l ) 820 a ~ 652 alJ
Observed*
129.31
129.96 132.11 133.01 134.65 135"05
136"60
137.45
138.40
141.00
182 or2] 820 as 652 a2 J 354 at 381 o~lJ 354 a2~ 381 a2J 164 a~ 571 at~ 643 a l ) 571 as~ 643 asJ 480 a 1
802 a l J
141.94 143,44 144.24 148-19 150.73 151.83 157"97
Line intensity
Calculatedt 129.17 129.30 129.37 129.39 129.77 129.90 129-98 129.99 132.18 132.82 133.13 134.58 135"00 135"09 135.26 136"53 136"58 136.74 136.77 137"25 137.30 137.46 137-49 137.57 138.15 138.31
138"46 138.54 140.87 141.05 141"19 141.67 141.86 142.00 143"28 143.41 144.15 144.28 148.20 150.59 150.79 151,69 151"90 157"83 158.10
Observed*
Calculated$
~0.4 4.5
2.0 0.8
0. i 0"1 0"3 !0"2 0.1
10.04 '0.1 0.1
0.8 1"8 1.3
6-0 broad
4.0
3"5 broad
4.5 broad
1.8 broad 4.5 broad 2.5 broad 3"3 broad
0.3 0.04 0.03 0-1 0"7 0"6 0"1 0-6 to.3 '0.3
t
0.04 0.3 0.4 0.3 0.2 0.3 0.2 0.3 0.4 0.5 0.1 0.2 0.2 0.5 0.5 0.3 0-2 0.6
6.0 broad 4.0 broad 4"0 broad
{°o::
Crystal structures and lattice parameters of the compounds of berkelium- 1V
1781
Table 2. (Contd.)
20 (deg)
hkl 723 cq] 480 ct2] 802 a2~ 751 a , | 373 cq J
Observed*
Line intensity
Calculatedt 158"84 159"33 159'62 159.72 159.83
159"47
Observed*
3"0 broad
Calculated~ [ 0"3 0"3 0.2 0.3 0.1
*Two independent observers' averaged readings (20 values are +0.10 °) and averaged intensities on a scale from l0 to 0. tBased on the orthorhombic lattice parameters a0 = 6.7162A, bo = 7.1031 A, co == 4.4084A, and h(~) = 1.54178A, ~.(al) = 1.54051 A, and ~.(t~2) = 1.54433 A. ~tCalculated using the POWD intensity program|8|, assuming the atomic coordinates of YFz[4] for those of BkF~, and scaled such that the most intense line had I = 10-0.
Table 3. Line list and indexing for LaF.~-type trigonal BkF3 (J P-V I I, Film 2691 A) 20 (deg)
hkl
Observed*
002 110 111 112 300 113 004
24.84 25.44 28.44 35.84 44.92 46"02 51.12
302~ 2201 221 114 222 223 304
52"02
115~ 410J 411 224 412 006 330 413 116
54'02 57.82 58"72 66-22 70.30 71-20 72'80 76'20 76' 80 80"50 82.80 83.70 86.20
Line intensity
Calculatedt
Observed*
Calculated~:
24.88 25.49 28.42 35"92 44.92 46.06 51-05 52.03 52-35 54.01 57.90 58.80 66.30 70-32
8.0 7-0 10"0 5.5 9.0 9.0 4-0
3.5 2.5 10-0 1.3 3.4 4.3 0.5 {3.1 0.3 1-9 0-5 0.4 1"3 1'2
71-18 71-41 72-80 76.14 76.94 80.53 82.86 83 "68 86"14
6.0
8.0 7.5 4-0 4.0 7.0 6.0
7.0 3'0 3 "0 I "5 3.0 6.5 4'0 broad
{0'8 0'3 1.6 0-2 0-4 0-2 0.5 1.4 0-2
8. D. K. Smith, University of California Lawrence Radiation Laboratory Report, UCRL-7196 (1963).
1782
J. R. P E T E R S O N and B. B. C U N N I N G H A M Table 3. (Contd.)
20 (deg)
hkl 332} 225J 414 al 306 al 600 al 117 cq 334al 602 am~ 415 alJ 602 a2~ 415 a~J
Observed*
88'20 92.90 97" 18 99-58 103"48 104"18 104.98
Line intensity
Calculatedt 88"20 88"24 92.91 97"21 99'54 103"44 104'18 104"98 105.02
Observed*
7"0 4"0 5'0 3"5 3"0 3'0 6"0
125" 16
105"35 105"39 106-62 107"00 110"83 118" 12 118"60 120"93 121"59 122"44 125"27 125"44
4"0
441 a2~ 118 a2J
125"96
125'83 126"00
2"0
524 al 524 ot2 336 al 443 al 308 ai 308 a 2 417 al 417 a2 525 cq 525 a2 711 al 711 a2 444 al 712 al 712a2
129"36 130"06 135"06 139"76 140'66 141 '66 144"56 145.56 147.26 148-36 150"24 151"44 157"74 159-84 161"44
129"31 129-92 135" 10 139"71 140"73 141 "53 144"61 145"51 147.36 148.34 150"33 151"43 157"67 159"79 161"45
3"5 1"5 4"0 3"5 5"0 3"0 6"0 4.0 6"0 4.0 6'0 4"0 2"5 3"0 1"5
521 cq 521 a2 522 c~1 523 al 523 ct2 416 al 227al 604 c~1 441 al~ 118 oqJ
I05'38 106"58 107"08 110"78 118"08 118"58 120"98 121"56 122"36
4"0 5'0 3"0 2'0 6"0 4"0 1"5 3"0 3"0
Calculated:~ {0"8 0"5 0"2 0'5 0"2 0"3 0"4 ~0"4 t 0"6 .[0.2 [0.3 0'6 0"3 0"2 0"7 0'3 0"3 0'3 0'5 ~0"4 [ 0"1 ~0"2 [ 0"1 0"2 O-1 0"6 0"5 0"6 0"3 1' 1 0'5 1"2 0"6 1"3 0"6 0"3 0"6 0"3
*A single reading of the powder pattern (2 0 readings are _+0.10°). Observed intensities are on a scale of 10 to 0 and may be in error due to the presence of a second phase (orthorhombic BkFa). fBased on the trigonal lattice parameters a0 = 6.9899A, co= 7.1566A and ~.(~) = 1.54178A, h(al) = 1.54051 A, and,k(a2) = 1.54433A. :[:Calculated using the POWD intensity program[8], assuming the atomic co-ordinates of LaF3 [3] for those of BkFa, and scaled such that the most intense line had I = 1 0 . 0 .
Crystal structures and lattice parameters of the compounds of berkelium- IV
1783
Thoma and Brunton studied the equilibrium dimorphism of the lanthanide trifluorides [9]. Dimorphism was not observed for the trifluorides of La through Nd. They determined equilibrium inversion temperatures for the trifluorides of Sm through Lu and found them to range from 555°C for SmFa to 1075°C for ErFa. The orthorhombic BkFa samples in this work were easily converted to the trigonal form by annealing at 600°C. The inversion temperature of BkFa lies between 350 and 600°C but could not be determined more precisely, since long-term annealings of trigonal BkF3 samples failed to produce significant transformations to the orthorhombic form. Table 4. Lattice parameters and ionic radii derived from the lanthanide and actinide trifluorides Lattice parameters (,4) Trifluoride
Structure type
a0
La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu Ac U Np Pu Am Cm Bk Bk Cf
LaF3 LaF~ LaF:~ LaF3 LaFz YF3 YF3 YF3 YF3 YF:~ YF3 YF,~ YF3 YF3 YF3 LaFa LaF3 LaFz LaFa LaF3 1-aFa LaFz YF3 YF~
7.186 7.112 7.075 7-030 6-970 6.669 6-622 6.570 6.513 6-460 6.404 6.354 6.283 6.216 6. ! 51 7-41 7-181 7-129 7.093 7.044 6-999 6-97 6.70 6.653
b0
7.059 7.019 6.984 6-949 6.906 6.875 6.846 6.811 6.786 6.758
7.09 7-041
co
Reference
M a+ ionic radius* (,4) (CN = 6)
7.352 7.279 7.238 7-200 7-188 4.405 4-3% 4.393 4.384 4-376 4.379 4.380 4.408 4.434 4-467 7-55 7.348 7.288 7.254 7.225 7" 179 7-14 ~ 4-41 / 4-395
10 7 11 10 12 4 4 4 4 4 4 4 4 4 4 13 13 13 13 14 14 this work 6
1-006 0.982 0-%8 0-955 0.945 0.921 0.909 0-900 0.888 0.877 0.868 0.860 0.855 0.851 0.848 1.076 1.005 0.986 0-974 0-%2 0-946 0.935 0-928 0.915
*Calculated according to the following formula: Ionic radius = (weight - averaged M - - F bond distance) -- 1-33 - 0.11 where the fluoride ionic radius is taken to be 1.33A [131 and the 9-fold to 6-fold co-ordination correction number is taken to be 0.11 A [ 13]. 9. R. E. Thoma and G. D. Brunton, lnorg. Chem. 5, 1937 (1966). 10. E, Staritzky and L. B. Asprey, Analyt. Chem. 29, 856 (1957). 11. H. E. Swanson, N. T. Gilfrich and G. M. Ugrinic, National Bureau of Standards Circular No. 539, Vol. 5 (1955). A S T M X - R a y Diffraction CardNo. 6-0325. 12. Fritz Weigel, Priiparative und r6ntgenographische Untersuchungen an stark radioaktiven Stoffen, University of Munich, MOniGh (1965). 13. W. H. Zachariasen, The Actinide Elements, Chap. 18, pp. 769-796, National Nuclear Energy Series, Vol. IV-14A. McGraw-Hill. New York (1954). 14. L, B. Asprey, T. K. Keenan, and F. H. Kruse, lnorg. Chem. 4, 985 (1965).
1784
J . R . PETERSON and B. B. C U N N I N G H A M
A summary of the pertinent crystallographic data of the lanthanide and actinide trifluorides along with calculated ionic radii is presented in Table 4. Crystallographic data for the high-temperature form of the heavier lanthanide trifluorides are given in Ref. [9]. The trifluorides of Bk and Cf are the first of the actinide trifluorides to be prepared in the YF3-type orthorhombic modification. By comparing the Bk ~+ ionic radius, as calculated from the LaFa-type trifluoride, to the similarly calculated ionic radii of the light lanthanides, it is seen that the Bk 3+ radius fits in after Pm, the last lanthanide to exhibit the trigonal trifluoride structure below -550°C. Alternatively, by comparing the Bk 3+ ionic radius, as calculated from the YF3-type trifluoride, to the similarly calculated ionic radii of the heavier lanthanides, it is seen that the Bk 3+ radius fits in before Sm, the first lanthanide to exhibit the YF3-type orthorhombic trifluoride structure. These calculations and comparisons are consistent with the observed dimorphism in the BkF3 system. It is important to note that comparisons of ionic radii can only be made meaningful if the values compared are calculated in like fashion from the same type of compound, both with respect to composition and crystal structure. From the data in Table 4 and by analogy with the work of Thoma and Brunton [9], one can predict that CfF3 will exhibit the LaF3-type trigonal structure at temperatures greater than or equal to about 700°C. The calculated density (X-ray) of YF3-type orthorhombic BkF3 is 9.70 g/cc, whereas for the LaF3-type trigonal modification, it is 10.15g/cc. These numbers reflect the general trend noted in the lanthanide trifluorides that the high-temperature, trigonal modification is the more dense one. Acknowledgements-The authors gratefully acknowledge the film reading assistance of Miss Judy Copeland and Mr. David Temple and the careful monitoring assistance of Mrs. Gertrude Bolz. This work was performed under the auspices of the U.S. Atomic Energy Commission.
CRYSTAL STRUCTURES AND LATTICE PARAMETERS OF THE COMPOUNDS OF B E R K E L I U M - IV BERKELIUM TRIFLUORIDE* J. R. P E T E R S O N t and B. B, C U N N I N G H A M Department of Chemistry and Lawrence Radiation Laboratory, University of California, Berkeley, California ( R e c e i v e d 1 D e c e m b e r 1967)
Abstract-BkF:~ has been found to exhibit a low-temperature, YFa-type orthorhombic structure and a high-temperature, LaF3-type trigonal structure. The lattice parameters of these two BkF:~ modifications are: a0 = 6"70-+0'01 A, bo = 7"09+-0"01 A, co = 4.41 +_0.01,4 (orthorhombic), and a0 = 6.97_+0.01A, c0=7.14_+0.01A (trigonal), where the error limits reflect the uncertainties in the derivation of the lattice parameters. The inversion temperature of BkF3 lies in the range 350 to 600°C. INTRODUCTION
TUE PREPARATION and crystallographic characterization of two structural forms
of berkelium trifluoride are described in this paper. EXPERIMENTAL The berkelium used in this work was derived from two separate purification cycles, both carried out as described previously[l]. Mass analyses of the two berkelium solutions showed the Ce and Nd contents to be 0.27 atom per cent Ce and 0.06 atom per cent Nd in one Bk solution, as contrasted with 9-53 atom per cent Ce and 0.03 atom per cent Nd in the other. The difference is attributed to the failure of the alcoholic HCI column, used to separate Bk and Ce, in the second purification cycle. The presence of the cerium and californium (from decay of 249Bk at a rate of - 0-2 per cent per day) contaminants prevented the determination of accurate lattice parameters for BkFa. Berkelium trifluoride samples were prepared by treatment of the oxides (stuck on a 5-rail Pt wire inside a hole in a ~-in Pt rod) with a one-to-two H2cgrHF~g) mixture at 600°C for ½hr, followed by a second, similar treatment with a fresh H2~grHFig) mixture. The trifluoride samples were either cooled rapidly to obtain the high-temperature, LaFa-type trigonal modification, or cooled slowly to obtain the low-temperature, YF~-type orthorhombic modification. In both cases the samples were cooled in the reaction gas mixture and then flushed with argon gas before removal from the all-Monel vacuum system. The very pale yellow-green trifluoride samples were "chipped off" the Pt wire into a quartz capillary, which was subsequently evacuated and sealed off for X-ray examination. Further details of the hydrofluorination techniques can be found in Ref. [2]. X-ray exposure times, using the same diffraction equipment and operating conditions as reported for the oxide work[l], were from eight to twelve hr on the 0.2/~g BkFa samples. *The experimental work reported here is taken from a thesis submitted by J. R. Peterson to the Graduate Division of the University of California in partial fulfillment of the requirements for the degree of Doctor of Philosophy. tPresent address: Department of Chemistry, The University of Tennessee, Knoxville, Tennessee 37916. 1. J. R. Peterson and B. B. Cunningham, inorg, nuel. Chem. Left. 3, 327 (1967). 2. J. R. Peterson, (Ph.D. Thesis), University of California Lawrence Radiation Laboratory Report, UCRL-17875 (October 1967). 1775
1776
J.R.
PETERSON RESULTS
a n d B. B. C U N N I N G H A M AND
DISCUSSION
Berkelium trifluoride was found to exist in both the LaF3-type trigonal structure[3], characteristic of the lanthanide trifluorides of La through Pro, and the YF3-type orthorhombic structure[4], characteristic of the lanthanide trifluorides of Sm through Lu. All of the BkF3 powder patterns showed the presence of more than one phase. Usually all the lines were accounted for by a trigonal trifluoride phase plus an orthorhombic trifluoride phase, but in some cases other, unaccounted-for lines were present in the powder patterns. One phase was always dominant, however, and only the more intense lines of the other phases were observed. Because of the possible superposition of lines belonging to different trifluoride phases, the observed line intensities for each separate phase are subject to error. In one case (JP-VII, Film 2691A) enough of the minor YF~-type orthorhombic phase was observed to determine lattice parameters for it. The observed lattice parameters of the individual trifluoride preparations along with their 24aCf and Ce contents are listed in Table I. Since CeF3 does not exhibit an orthorhombic modification, the YF3-type berkelium trifluoride lattice parameters were initially corrected for the known Cf content of the Bk sample in accordance with Vegard's Law[5]. The lattice parameters of orthorhombic CfFa (ao = 6-653 ± 0.002 A, b0 = 7.041 ___0.002 A, and Co = 4.395 __+0.001 A) were derived from a single preparation by Peterson et al. [6]. These "corrected-forCf", orthorhombic BkFa lattice parameters were then plotted vs. the Ce content of the berkelium sample and extrapolated to zero Ce content to obtain "best Table 1. Berkelium trifluoride lattice parameters
Sample number
Film number
Structure type
z49Cf* content (atom %)
Total Cet content (atom %)
Observed lattice parameters~; (,4) a0 -+ 2o-
JRP-XXIII JP-VII JP-X JRP-XXI JRP-XXII JP-VII JP-X JP-X
2624A 2691A 2713A 2614A 2619A 2691A 2716A 2734A
YFa YF a YF~ LaF3 LaFa LaFa LaFa LaFs
7-03 1.53 5-16 5.26 6-20 1-53 5.79 8-05
0.27 9.53 9.53 0.27 0.27 9.53 9.53 9.53
6.695-4-0.004 6.717-+0.015 6.716-+0.001 6.973-+0.002 6.965-+0.003 6-990-+0.001 6.990±0.001 6.988-+0.001
bo -+ 2 o-
c0-+ 2Gr
7.086--_0-004 4.407-+0.003 7.114-----0.011 4.409-+0.005§ 7-103 -+0.001 4.408-+0.001 7-143 ~0.003 7.140±0.003 7.157-+0.001 7.158---0.002 7.156±0.002
*Calculated assuming 24*Bkhalf-life is 314 days. tDetermined by mass analysis. See text. :[:Lattice parameters are the least squares value. The 2 o- error limits represent the 95 per cent confidence range reflecting only the internal consistency of the data for the individual preparation. §The second phase in a predominantly trigonal BkFa powder pattern.
3. Allan Zalkin, D a v i d H. Templeton, and T e d E. Hopkins, lnorg. Chem. 5, 1466 (I966). 4. Allan Zalkin and D. H. Templeton, J.Am. chem. Soc. 75, 2453 (1953). 5. A. F. Wells, Structural Inorganic Chemistry, Chapter X X V I I , pp. 9 7 1 - 1 0 2 8 . Oxford University Press, London (1962). 6. J. R. Peterson, J. C. Copeland, and D. Temple, University of California Lawrence Radiation Laboratory, Unpublished results (1967).
Crystal structures and lattice parameters of the compounds of berkelium - IV
1777
estimates" for the lattice parameters of orthorhombic BkF3:a0 = 6.70___ 0.01 A, b0 = 7.09+__0.01A, and co = 4.41--4-_0.01A, where the error limits reflect the uncertainties in the derivation of the lattice parameters. Similarly for LaF3-type trigonal berkelium trifluoride, since the trigonal modification of CfF3 is unknown, the lattice parameters were corrected for the known Ce content of the Bk sample using the parameters of Swanson et al. (a0 = 7.112A and co = 7.279A)[7]. These "corrected-for-Ce," trigonal BkF:~ lattice parameters did not vary in any regular fashion as the Cf content of the berkelium sample increased, so they were just averaged to obtain "best estimates" for the lattice parameters of trigonal BkF3: a0 = 6 . 9 7 _ 0.01 A and Co = 7- 14___ 0.01 A, where again the lattice parameters are rounded off to the nearest hundredth and the error limits reflect the uncertainties in the derivation of the lattice parameters. The Miller indices, observed and calculated 2 0 values, and observed and calculated line intensities for one sample of each type of BkF:~ are given in Tables 2 and 3. Table 2. Line list and indexing for YF3-type orthorhombic BkF3 (J P-X, Film 2713A) 20 (deg)
Line intensity
Observed*
Calculatedt
Observed*
Calculated~
011 101 020 200 111 210 201 121 211 002 221
23.67 24.12 25"02 26-47 27.27 29.37 33.51 35.06 35.90 40-85 42.25
23.75 24.15 25.07 26.54 27.26 29.42 33-55 35.09 35.91 40.94 42.34
6.5 9.0 9.0 1.5 10.0 10.0 3.5 9.0 3.0 6.5 6-5
2.0 5-7 6.3 0.1 10.0 7,6 0.4 3.1 0.1 1.1 1-4
102~ 03 I J 112
43.14
43.20 43-38 45.13
4.0
~0-4 t0' 1 1.8
301 ~ 131/ 230 311 022 122
45.44
45.44 45-53 46.95 47.30 48-61 50-60
10.0
212/ 0401 321 400 141
51.23
hkI
44.99
46.84 47.29 48.54 50.53
52"58 54"53 57-57
51.21 51"46 52-59 54'66 57-62
6.5
8.5 7-0 7.0 7.0 8.0 broad 7"5 5"5 6'0
~2-4 (3.6 3.2 1.8 1.5 1.4 {2.3 1"2 2"1 0"9 1-0
7. H. E. Swanson, N. T. Gilfrich, M. I. Cook, R. Stinchfield and P. C. Parks, National Bureau of Standards Circular No. 539, Vol, 8. U.S. Government Printing Office, Washington, D.C. (1959); AS T M X-RA Y Diffraction Card No. 8-45.
J. R. PETERSON and B. B. CUNNINGHAM
1778
Table 2. (Contd.)
20 (deg)
Line intensity
hkl
Observed*
Calculatedt
Observed*
Calculated$
302~ 132J 312/. 411[ 331J 420 241 232 013~ 322J 113 042 430 142~ 051J
58.82
5.8
88.28
58.79 58.87 60.35 60.42 60.68 61.04 62.84 64.03 64.78 64.91 66.44 67.76 68.51 69.38 69.52 69.87 70-50 70"79 71 '05 71"12 72"17 72"20 72'23 75'13 75"52 76" 14 76"26 78"38 79"29 81 "26 81"88 81.95 83'52 86.10 86.30 86.50 88.40
3.5 broad
{0.2 0.6 {0.7 0.4 0.9 1.0 0.3 1.1 {0.8 0.3 0.3 0.5 0-1 {0.4 0.1 0.6 0.4 {0'2 1"0 0"7 {0"2 0"6 0.2 0-8 1'2 ~0"8 10"4 0"6 0'3 0.4 {0"2 0"3 0"4 {0"7 0.4 0.6 0.5
413~ 522J
89.73
89.75 89.86
5-5 broad
{0.8 0.4
114~
91-78
91.63 91-88
5.0
352~ 45 lJ 062t 541 124J 532~ 162J
93.96
94.05 94.11 95.32 95.56 95.69 96.63 96.84
203 402 123]. 341~ 151J 332// 250} 431J 511 223 422~ 033J 440 521 060 342~ 152J 351 5311 161~ 252.1 610
243.1
60.37 61.02 62.77 64.01 64.76 66-31 67.65 68.45 69.35 69.80 70.40 71"05 72' 15 75"10 75"45 76"15 78-39 79' 19 81.23 81 "83 83"63 86-23
95-51 96.81
7.5 6.5 3.5 6-5 6-5 3.0 4.5 1.5 3.0 3.0 2.5 7"0 5"5 4'0 6"0 5"0 3'5 3.0 4"3 4"0 3-0 6.5 broad
3.5 broad 4.5 broad 1"5 broad
{0.4
0.7
{0.3 0.2 {0.2 0.2 0.4 {0.1 0.2
Crystal structures and lattice parameters of the compounds of berkelium- I V Table 2. (Contd.)
20 (deg) hkI
Observed*
053] 361J 630] 343~ 153J 433 ~l 304 c~] 612 c~l~ 134 ~lJ 314~1] 171 c~1~ 270 ~1 460 c~1 542 c~1 542 c~2 551 ~1"~ 324a~J 551 ~ ] 324 c~2J 362 c~l 701 c~1 711 oq'~ 144 c~iJ 632al 533 cq| 172a1[ 334 c~d 721 cq 371 721 ~e 263 oq] 272 cq~ 1)80 c~1 462 c~1 650 ~1 712 a ~ 453 ~1) 712 ~" 561 cq 453 c~ 344 623 154 c~ 181 c~ 344 a2 623 ~z 154 c~z 181 c~
al} l
98"26 99"36 100-51 102.36
103"91 104.95 105-50 106-09 106.59 107.84 108.29 109-09 110"54 112-29 113-79 115.04 116.39 116-78
Line intensity
Calculatedt 98.01 98.42 99-24 99.47 99.54 100.49 102-34 102.40 102.41 103.72 103.87 104-93 105.52 106-15 106.53 107.86 107.92 108.25 108.31 109.12 111).49 I 11.94 112.30 113.76 114.76 115.02 115.17 116.37
Observed*
4.0 2.5 broad 3.5 4-0
3-5 2-0 I-8 1.3
2.0 1-0 broad 2.0
2.0 3.5 3.0
126.20 126.24 126.34 126.72
5.8
126.82
126.76 126.80 126.90
3-0
124.52
0'1 0"2
3.0 broad
126.22
123.92
0"3 0'3 0'2 0'1
4.0
2.3
120-72 122.27
0-4 0.1 0-1 0"4 0-1 0-3 0"3
4-0
I 16.76 116.83 120.09 120.12 120.34 120.78 122-34 123.83 123.94 124.37 124-43 124.48 126.15
120.13
Calculatedt
5-5 3.0 1.8 5.0 3-0
0.3 O.I
t0:I
0.4
0.5 0.3 0.1 0.3 0-3 0.3 0.5 0.1 0.1 0.3 0-2 0-4 0.3 0-2 0.1 0.2 0.1 0.1
1779
1780
J. R. P E T E R S O N and B. B. C U N N I N G H A M Table 2. (Contd.)
20 (deg) h kI 205 al 1 372 a l l 471 a l l 504 a l l 205 a2] 372 a2[ 471 ot2[ 504 ~sJ 281 c~l 281 a2 800 a 073 a 810 oq 633 al 073 a2 225 cq" 741 cq 173 al 524 oqj 225 a2 ] 741 a2[ 173 a,~ 524 a 2 | 035 a l J 732 cq ] 035 as [ 562a1[ 082alJ 182 a l ) 820 a ~ 652 alJ
Observed*
129.31
129.96 132.11 133.01 134.65 135"05
136"60
137.45
138.40
141.00
182 or2] 820 as 652 a2 J 354 at 381 o~lJ 354 a2~ 381 a2J 164 a~ 571 at~ 643 a l ) 571 as~ 643 asJ 480 a 1
802 a l J
141.94 143,44 144.24 148-19 150.73 151.83 157"97
Line intensity
Calculatedt 129.17 129.30 129.37 129.39 129.77 129.90 129-98 129.99 132.18 132.82 133.13 134.58 135"00 135"09 135.26 136"53 136"58 136.74 136.77 137"25 137.30 137.46 137-49 137.57 138.15 138.31
138"46 138.54 140.87 141.05 141"19 141.67 141.86 142.00 143"28 143.41 144.15 144.28 148.20 150.59 150.79 151,69 151"90 157"83 158.10
Observed*
Calculated$
~0.4 4.5
2.0 0.8
0. i 0"1 0"3 !0"2 0.1
10.04 '0.1 0.1
0.8 1"8 1.3
6-0 broad
4.0
3"5 broad
4.5 broad
1.8 broad 4.5 broad 2.5 broad 3"3 broad
0.3 0.04 0.03 0-1 0"7 0"6 0"1 0-6 to.3 '0.3
t
0.04 0.3 0.4 0.3 0.2 0.3 0.2 0.3 0.4 0.5 0.1 0.2 0.2 0.5 0.5 0.3 0-2 0.6
6.0 broad 4.0 broad 4"0 broad
{°o::
Crystal structures and lattice parameters of the compounds of berkelium- 1V
1781
Table 2. (Contd.)
20 (deg)
hkl 723 cq] 480 ct2] 802 a2~ 751 a , | 373 cq J
Observed*
Line intensity
Calculatedt 158"84 159"33 159'62 159.72 159.83
159"47
Observed*
3"0 broad
Calculated~ [ 0"3 0"3 0.2 0.3 0.1
*Two independent observers' averaged readings (20 values are +0.10 °) and averaged intensities on a scale from l0 to 0. tBased on the orthorhombic lattice parameters a0 = 6.7162A, bo = 7.1031 A, co == 4.4084A, and h(~) = 1.54178A, ~.(al) = 1.54051 A, and ~.(t~2) = 1.54433 A. ~tCalculated using the POWD intensity program|8|, assuming the atomic coordinates of YFz[4] for those of BkF~, and scaled such that the most intense line had I = 10-0.
Table 3. Line list and indexing for LaF.~-type trigonal BkF3 (J P-V I I, Film 2691 A) 20 (deg)
hkl
Observed*
002 110 111 112 300 113 004
24.84 25.44 28.44 35.84 44.92 46"02 51.12
302~ 2201 221 114 222 223 304
52"02
115~ 410J 411 224 412 006 330 413 116
54'02 57.82 58"72 66-22 70.30 71-20 72'80 76'20 76' 80 80"50 82.80 83.70 86.20
Line intensity
Calculatedt
Observed*
Calculated~:
24.88 25.49 28.42 35"92 44.92 46.06 51-05 52.03 52-35 54.01 57.90 58.80 66.30 70-32
8.0 7-0 10"0 5.5 9.0 9.0 4-0
3.5 2.5 10-0 1.3 3.4 4.3 0.5 {3.1 0.3 1-9 0-5 0.4 1"3 1'2
71-18 71-41 72-80 76.14 76.94 80.53 82.86 83 "68 86"14
6.0
8.0 7.5 4-0 4.0 7.0 6.0
7.0 3'0 3 "0 I "5 3.0 6.5 4'0 broad
{0'8 0'3 1.6 0-2 0-4 0-2 0.5 1.4 0-2
8. D. K. Smith, University of California Lawrence Radiation Laboratory Report, UCRL-7196 (1963).
1782
J. R. P E T E R S O N and B. B. C U N N I N G H A M Table 3. (Contd.)
20 (deg)
hkl 332} 225J 414 al 306 al 600 al 117 cq 334al 602 am~ 415 alJ 602 a2~ 415 a~J
Observed*
88'20 92.90 97" 18 99-58 103"48 104"18 104.98
Line intensity
Calculatedt 88"20 88"24 92.91 97"21 99'54 103"44 104'18 104"98 105.02
Observed*
7"0 4"0 5'0 3"5 3"0 3'0 6"0
125" 16
105"35 105"39 106-62 107"00 110"83 118" 12 118"60 120"93 121"59 122"44 125"27 125"44
4"0
441 a2~ 118 a2J
125"96
125'83 126"00
2"0
524 al 524 ot2 336 al 443 al 308 ai 308 a 2 417 al 417 a2 525 cq 525 a2 711 al 711 a2 444 al 712 al 712a2
129"36 130"06 135"06 139"76 140'66 141 '66 144"56 145.56 147.26 148-36 150"24 151"44 157"74 159-84 161"44
129"31 129-92 135" 10 139"71 140"73 141 "53 144"61 145"51 147.36 148.34 150"33 151"43 157"67 159"79 161"45
3"5 1"5 4"0 3"5 5"0 3"0 6"0 4.0 6"0 4.0 6'0 4"0 2"5 3"0 1"5
521 cq 521 a2 522 c~1 523 al 523 ct2 416 al 227al 604 c~1 441 al~ 118 oqJ
I05'38 106"58 107"08 110"78 118"08 118"58 120"98 121"56 122"36
4"0 5'0 3"0 2'0 6"0 4"0 1"5 3"0 3"0
Calculated:~ {0"8 0"5 0"2 0'5 0"2 0"3 0"4 ~0"4 t 0"6 .[0.2 [0.3 0'6 0"3 0"2 0"7 0'3 0"3 0'3 0'5 ~0"4 [ 0"1 ~0"2 [ 0"1 0"2 O-1 0"6 0"5 0"6 0"3 1' 1 0'5 1"2 0"6 1"3 0"6 0"3 0"6 0"3
*A single reading of the powder pattern (2 0 readings are _+0.10°). Observed intensities are on a scale of 10 to 0 and may be in error due to the presence of a second phase (orthorhombic BkFa). fBased on the trigonal lattice parameters a0 = 6.9899A, co= 7.1566A and ~.(~) = 1.54178A, h(al) = 1.54051 A, and,k(a2) = 1.54433A. :[:Calculated using the POWD intensity program[8], assuming the atomic co-ordinates of LaF3 [3] for those of BkFa, and scaled such that the most intense line had I = 1 0 . 0 .
Crystal structures and lattice parameters of the compounds of berkelium- IV
1783
Thoma and Brunton studied the equilibrium dimorphism of the lanthanide trifluorides [9]. Dimorphism was not observed for the trifluorides of La through Nd. They determined equilibrium inversion temperatures for the trifluorides of Sm through Lu and found them to range from 555°C for SmFa to 1075°C for ErFa. The orthorhombic BkFa samples in this work were easily converted to the trigonal form by annealing at 600°C. The inversion temperature of BkFa lies between 350 and 600°C but could not be determined more precisely, since long-term annealings of trigonal BkF3 samples failed to produce significant transformations to the orthorhombic form. Table 4. Lattice parameters and ionic radii derived from the lanthanide and actinide trifluorides Lattice parameters (,4) Trifluoride
Structure type
a0
La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu Ac U Np Pu Am Cm Bk Bk Cf
LaF3 LaF~ LaF:~ LaF3 LaFz YF3 YF3 YF3 YF3 YF:~ YF3 YF,~ YF3 YF3 YF3 LaFa LaF3 LaFz LaFa LaF3 1-aFa LaFz YF3 YF~
7.186 7.112 7.075 7-030 6-970 6.669 6-622 6.570 6.513 6-460 6.404 6.354 6.283 6.216 6. ! 51 7-41 7-181 7-129 7.093 7.044 6-999 6-97 6.70 6.653
b0
7.059 7.019 6.984 6-949 6.906 6.875 6.846 6.811 6.786 6.758
7.09 7-041
co
Reference
M a+ ionic radius* (,4) (CN = 6)
7.352 7.279 7.238 7-200 7-188 4.405 4-3% 4.393 4.384 4-376 4.379 4.380 4.408 4.434 4-467 7-55 7.348 7.288 7.254 7.225 7" 179 7-14 ~ 4-41 / 4-395
10 7 11 10 12 4 4 4 4 4 4 4 4 4 4 13 13 13 13 14 14 this work 6
1-006 0.982 0-%8 0-955 0.945 0.921 0.909 0-900 0.888 0.877 0.868 0.860 0.855 0.851 0.848 1.076 1.005 0.986 0-974 0-%2 0-946 0.935 0-928 0.915
*Calculated according to the following formula: Ionic radius = (weight - averaged M - - F bond distance) -- 1-33 - 0.11 where the fluoride ionic radius is taken to be 1.33A [131 and the 9-fold to 6-fold co-ordination correction number is taken to be 0.11 A [ 13]. 9. R. E. Thoma and G. D. Brunton, lnorg. Chem. 5, 1937 (1966). 10. E, Staritzky and L. B. Asprey, Analyt. Chem. 29, 856 (1957). 11. H. E. Swanson, N. T. Gilfrich and G. M. Ugrinic, National Bureau of Standards Circular No. 539, Vol. 5 (1955). A S T M X - R a y Diffraction CardNo. 6-0325. 12. Fritz Weigel, Priiparative und r6ntgenographische Untersuchungen an stark radioaktiven Stoffen, University of Munich, MOniGh (1965). 13. W. H. Zachariasen, The Actinide Elements, Chap. 18, pp. 769-796, National Nuclear Energy Series, Vol. IV-14A. McGraw-Hill. New York (1954). 14. L, B. Asprey, T. K. Keenan, and F. H. Kruse, lnorg. Chem. 4, 985 (1965).
1784
J . R . PETERSON and B. B. C U N N I N G H A M
A summary of the pertinent crystallographic data of the lanthanide and actinide trifluorides along with calculated ionic radii is presented in Table 4. Crystallographic data for the high-temperature form of the heavier lanthanide trifluorides are given in Ref. [9]. The trifluorides of Bk and Cf are the first of the actinide trifluorides to be prepared in the YF3-type orthorhombic modification. By comparing the Bk ~+ ionic radius, as calculated from the LaFa-type trifluoride, to the similarly calculated ionic radii of the light lanthanides, it is seen that the Bk 3+ radius fits in after Pm, the last lanthanide to exhibit the trigonal trifluoride structure below -550°C. Alternatively, by comparing the Bk 3+ ionic radius, as calculated from the YF3-type trifluoride, to the similarly calculated ionic radii of the heavier lanthanides, it is seen that the Bk 3+ radius fits in before Sm, the first lanthanide to exhibit the YF3-type orthorhombic trifluoride structure. These calculations and comparisons are consistent with the observed dimorphism in the BkF3 system. It is important to note that comparisons of ionic radii can only be made meaningful if the values compared are calculated in like fashion from the same type of compound, both with respect to composition and crystal structure. From the data in Table 4 and by analogy with the work of Thoma and Brunton [9], one can predict that CfF3 will exhibit the LaF3-type trigonal structure at temperatures greater than or equal to about 700°C. The calculated density (X-ray) of YF3-type orthorhombic BkF3 is 9.70 g/cc, whereas for the LaF3-type trigonal modification, it is 10.15g/cc. These numbers reflect the general trend noted in the lanthanide trifluorides that the high-temperature, trigonal modification is the more dense one. Acknowledgements-The authors gratefully acknowledge the film reading assistance of Miss Judy Copeland and Mr. David Temple and the careful monitoring assistance of Mrs. Gertrude Bolz. This work was performed under the auspices of the U.S. Atomic Energy Commission.