New hydrides of ternary intermetallics based on Zr with Fe, Co, Ni and Sn or Sb

\ PERGAMON

International Journal of Hydrogen Energy 13 "0888# 788Ð896

New hydrides of ternary intermetallics based on Zr with Fe\ Co\ Ni and Sn or Sb L[G[ Akselruda\\ D[ Fruchartb\ N[D[ Koblyuka\ O[ Isnardb\ G[A[ Melnyka\ R[V[ Skolozdraa a b

Department of Chemistry\ Ivan Franko State University\ 189994\ Lviv\ Ukraine Laboratoire de Cristallo`raphie\ CNRS\ BP 055 27939\ Grenoble cedex 8\ France

Abstract A series of hydrides based on the alloys Zr5M?0[4X0[4 "M?  Fe\ Co\ Ni\ X  Sn\ Sb# and Zr5NiAl1 have been synthesized "conditions of hydrogenation] T  029>C\ PH1  19 MPa# and their crystal structures have been determined using both X!ray and neutron di}raction[ During hydrogenation the crystal structure of Zr5M?0[4Sb0[4 and Zr5Fe0[4Sn0[4 changes from the Fe1P type to the Ni2P type "Zr4M?X1H½00#[ The hydrogen atoms occupy eight sites\ six of those have a tetrahedral coordination whereas two H atoms occupy trigonal bipyramids[ The structure of Zr5NiAl1D6[4 "and Zr5NiAl1H8[5# has a doubled c cell parameter reference to the starting alloy^ it belongs to the Zr5FeAl1D09 structure type[ Þ 0888 Published by Elsevier Science Ltd on behalf of International Association for Hydrogen Energy[ All rights reserved[

0[ Introduction Compounds exhibiting the Fe1P structure type "space group P5¹1m# form a large series of intermetallics\ par! ticularly in the ternary systems MM?X composed of two transition metals M "IVÐV groups# and M? "VIII group# and of elements X of the IIIBÐVB groups "i[e[ Sn\ Sb#\ or RMX\ where R is a rare earth metal ð0Ł[ This structure contains empty tetrahedra and trigonal bipyramids\ which are potential interstitial sites able to accommodate hydrogen atoms[ For example ZrNiAl is characterized by a superstructure directly related to the Fe1P type ð1Ł\ it exhibits an absorption capacity of 9[2 H:f[u[ "f[u[  formula unit# ð2Ł[ The RNiAl alloys absorb much more hydrogen than ZrNiAl\ from 0[0Ð0[3 H:f[u[\ depending on R[ Hydrogenation of these compounds provokes an orthorhombic distortion of the hexagonal structure ð3\ 4Ł[ For the point of view of hydrogen storage\ a large interest results from compounds of this series\ containing a dominant amount of zirconium\ transition metals and aluminum "Zr5M?Al1\ M?  Fe\ Co\ Ni ð5\ 6Ł#[ Belonging to this series a new hydride Zr5FeAl1H09 was

recently stabilized ð7Ł[ The structure of the corresponding deuteride "space group P5¹1c# derives from the Zr5FeAl1 host structure "space group P5¹1m#[ However there are correlated little displacements of the metal atoms owing to the starting compounds\ leading to a doubling of the c parameter[ The deuterium atoms occupy three tetra! hedral and one trigonal bipyramid sites and do not bond directly with aluminum[ New Fe1P types of alloys having similar composition have been stabilized with X  Sn and Sb ð8Ł[ The crystal structure of Zr5Co0[44Sn0[34 was investigated by single crystal method and exhibits some statistical distribution of cobalt and tin ð09Ł[ More recently hydrides of R5M?Al1 and R5M?Sn1 have been reported[ They were synthesized at room temperature and under a gas pressure of 9[0 MPa and the hydrogen content varies from 8[3 to 09[7 H:f[u[ ð00\ 01Ł[ Their crystal structure belongs to the Zr5FeAl1D09 type[ In this paper we present the results of hydrogenation of Zr5M0[4Sn0[4 and Zr5M0[4Sb0[4 alloys and the study of the hydride crystal structures[ 1[ Experimental

 Corresponding author

The alloys were prepared by melting together the com! ponents using an arc furnace under a puri_ed argon

9259!2088:88:,19[99 Þ 0888 Published by Elsevier Science Ltd on behalf of International Association for Hydrogen Energy[ All rights reserved PII] S 9 2 5 9 ! 2 0 8 8 " 8 7 # 9 9 0 5 4 ! 6

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atmosphere[ The alloys were annealed in evacuated quartz ampoules at 599>C for about 299 h[ X!ray powder di}raction data of the starting samples and the cor! responding hydrides were measured using a BraggÐBren! tano geometry di}ractometer equipped backscattering graphite monochromator\ at wavelength of CuÐKa radi! ation[ Hydrogenation "deuteration# was achieved in dedi! cated stainless steel autoclaves[ The hydrogen gas pres! sure as well as temperature "if heating is needed to acti! vate the reaction# were controlled within the ranges 9Ð2 MPa and 19Ð079>C\ respectively[ Neutron di}raction experiments were carried out at the high ~ux reactor of the Institute Laue!Langevin "Grenoble#\ using the D0B position sensitive detector "CNRS!CRG#[ Powder di}raction patterns were rec! orded using the wavelength issued from a focusing pyr! olitic graphite monochromator "l  1[421 _# on an 79> Bragg angle range[ Re_nements of the structure par! ameters were achieved using the CSD program ð02Ł[

2[ Results and discussion 2[0[ The Sb compounds As starting materials for hydrogenation we have used samples of Zr5M?0[4Sb0[4 composition[ The X!ray data shows dominant Fe1P type of patterns plus insigni_cant amounts of impurity phases[ The cell parameters of the main phases "Fe1P type# are listed in Table 0[ Owing to the analysis of datas obtained on the Zr5M?0[4X0[4 com! pounds both from single crystal analysis ð09Ł and from the powder method\ it can be stressed that a solid solution with the substitutions of M? and X would exist on a given extend[ That suggests a Zr5M?0[42xX0[42x general formula with compositions from the X side limited to Zr5M?X1[ The richest Co content would correspond to the single crystal composition Zr5Co0[54Sn0[24[ In most cases\ the hydrogenation process does not take place at room temperature under a 1 MPa H1 "D1# gas pressure[ Then at 029>C a drastic drop of pressure is observed\ indicating that hydrogenation proceeds very quickly\ the most reactive sample being Zr5Ni0[4Sb0[4[ The hydrogen uptakes of the starting alloys were calculated weighing before and after hydrogenation[ From 8Ð00 H atoms per f[u[ were absorbed[ X!ray patterns of the Zr5Fe0[4Sb0[4 sample as recorded before and after hydrogenation are shown in Fig[ 0[ It is noteworthy that the X!ray and neutron di}raction patterns of the Zr5Fe0[4Sb0[4 hydride di}er completely from that of the starting compound[ The strongest Bragg re~ections of the patterns were indexed on the basis of a tetragonal lattice with approximate cell parameters a  00[05 and c  4[62 _[ The existence rule for the re~ections corresponds to the space group I3¹[ The metal

Table 0 Crystallographic data of the compounds before and after hydro! genation Compound

Space group

Cell parameters in _ a

Zr5NiAl1 Zr5NiAl1H8[5 "H09# Zr5NiAl1D6[4 "D6#

P5 Þ1m P5 Þ1c P5 Þc

Zr5Fe0[4Sn0[4 Zr4FeSn1H½00[2 "H8[6# Zr5Co0[4Sn0[4 Zr5Co0[4Sn0[4H½09[0 "H8[4# Zr5Ni0[4Sn0[4 Zr5Ni0[4Sn0[4H½09[4 "H09[4# Zr5Fe0[4Sb0[4 Zr4FeSb1H00[2 "H8# Zr5Co0[4Sb0[4 Zr5CoSb1H½00[2 "H00# Zr4Ni0[4Sb0[4 Zr5NiSb1H½00[2 "H09#

c

6[822"1# 7[029"2# 7[017"0#

2[257"0# 6[029"2# 6[064"0#

P5 Þ1m I3 Þ P5 Þ1m P5 Þ1m P5 Þ1m P5 Þ1m

6[882"2# 00[167"3# 6[831"1# 7[037"1# 6[898"1# 7[095"2#

2[356"1# 4[624"2# 2[404"0# 2[5695"6# 2[434"0# 2[546"1#

P5 Þ1m I3 Þ P5 Þ1m I3 Þ P5 Þ1m I3 Þ

6[644"1# 00[046"2# 6[659"2# 00[051"4# 6[630"0# 00[043"1#

2[562"0# 4[618"1# 2[579"1# 4[608"2# 2[5662"7# 4[608"1#

 The re_ned amount of hydrogen agrees with the mass deter! mination "Hx#[  Or P5 Þ1c[

substructure is of the Ni2P type[ The position parameters of the metal and hydrogen sites were re_ned _rst from neutron powder di}raction on the iron compound[ The observed\ calculated and di}erence neutron patterns of the hydride are shown in Fig[ 1 and the results of the structure re_nement are listed in Table 1[ The rather high values of the obtained R!factors are due to the presence of some amount of impurity phases[ In the hydride structure there are two kinds of sites occupied by Zr only "labelled Zr0 and Zr2# both having the 7` position[ A third 7` position is occupied stat! istically by Zr and Fe atoms in a ratio close to 0 ] 0[ Eight types of hydrogen positions are distributed on six tetrahedral and two trigonal bipyramidal sites[ The environments of the H atoms are] tetrahedra with H0! ð3"Zr\ Fe#Ł\ H1!ð3ZrŁ\ H3!ðZr\ 1"Zr\ Fe#\ SbŁ\ H4! ð2Zr\ "Zr\ Fe#Ł\ H5!ð1Zr\ 1"ZrFe#Ł\ H7!ð1Zr\ "Zr\ Fe#SbŁ and bipyramids with H2!ð2Zr\ 1SbŁ and H6! ð2Zr\ "Zr\ Fe#\ SbŁ[ The H2 and H7 sites are occupied partly[ Thus the compound formula can be written as Zr4FeSb1H00[2 in good agreement with the experimental determination "¼00#[ The interatomic distances are listed in Table 2[ Some MÐH and HÐH distances appear rather short "e[g[ involv! ing H7# and can be explained by the partial occupation of the hydrogen sites with too high a standard deviation[ This means that the _nal H content should be a little less

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Fig[ 0[ X!ray di}raction patterns of Zr5Fe0[4Sb0[4 before "a# and after "b# hydrogenation[ The stars show the Si re~ections used for calibration[

Fig[ 1[ Observed "dots#\ calculated "line# and di}erence neutron di}raction patterns of the Zr4FeSb1H00[2 hydride[

than indicated above[ As shown in ð01Ł\ calculation of the electronic structure of Zr5M?X1Hx compounds allows to range the charge on hydrogen from 9[94Ð9[15 electrons per atoms\ that leads to a marked limitation of its e}ective

radius[ The coordination polyhedra of the di}erent H sites all linked by edges and tops only "Fig[ 2#[ The X!ray patterns of Zr4CoSb1Hx and Zr4NiSb1Hx show rather broad di}raction lines as a result of a less

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Table 1 Re_ned parameters from the neutron powder di}raction data of Zr4FeSn1H00[2 Atom

Site

x:a

y:b

z:c

Zr0 Zr1 Zr2 Sb H0 H1 H2 H3 H4 H5 H6 H7

7` 7` 7` 7` 1d 1a 7` 7` 7` 7` 7` 7`

9[971"2# 9[258"2# 9[193"2# 9[142"3# 0:1 9 9[709"7# 9[508"5# 9[109"4# 9[556"5# 9[149"5# 9[656"05#

9[019"2# 9[926"2# 9[139"3# 9[918"8# 9 9 9[052"6# 9[951"5# 9[957"6# 9[099"5# 9[012"09# 9[995"01#

9[006"4# 9[882"5# 9[670"5# 9[379"09# 2:3 9 9[425"09# 9[128"09# 9[771"00# 9[715"02# 9[004"00# 9[008"19#

B"is:eq#  0[5"3#[ Occupations] Zr1\ 9[4Zr¦9[4Fe^ H2\ 9[58"4#H^ H7\ 9[34"02#H[ RI "intensity#\ RP "pro_le#] RI  9[0163\ RP  9[1712[

stable state of these formulations\ allowing the pre! cipitation of some other phases not present in the starting samples[ Consideration with the stability of multinary phases in the ZrÐCoÐSb and ZrÐNiÐSb systems\ presently we have no information on the existence of ternaries such as Zr4CoSb1 and Zr4NiSb1\ whereas Zr4FeSb1 exists at the light of preliminary data[ The cell volume of Zr4 CoSb1Hx and Zr4NiSb1Hx are close to that of Zr4FeSb1H00[2\ thus suggesting similar formulas for the Co and Ni hydrides "H½00#[ 2[1[ The Sn compounds Comparison with the Sb compounds\ the Sn starting alloys Zr5M?0[4Sn0[4 were found heterogeneous[ Besides the main phase of Fe1P type\ other phases were identi_ed as Zr4Sb2 and some free Zr[ Samples with di}erent ratio Sn to M? were prepared also\ however all the samples were found heterogeneous as well[ The Zr5M?0[4Sn0[4 com! position leads to the best samples therefore\ it has been retained for further investigations[ As for the Zr5M?0[4Sb0[4 alloys\ hydrogenation of the

Table 2 Selected interatomic distances "_# in for Zr4FeSn1H00[2 Zr0

0[65"3# 0[77"7# 0[84"7# 1[94"6#

0 H7 0 H7 0 H1 0 H2

1[09"04# 1[01"06# 1[04"5# 1[21"6#

1 Zr0 0 Zr2 1 Sb 0 Zr2

1[55"4# 1[60"4# 2[90"6# 2[91"4#

0 Zr1 0 Zr0 0 Zr1

2[04"4# 2[14"5# 2[30"4#

Zr1 0 H7 0 H6 0 H3 0 H5 0 H4

0[60"06# 0[67"8# 0[68"6# 0[74"7# 0[81"5#

0 H3 0 H0 0 Sb 0 Zr1 0 Sb

0[84"6# 1[95"2# 1[85"6# 2[93"3# 2[96"5#

0 Zr2 0 Zr0 0 Zr2 0 Sb 0 Zr2

2[09"4# 2[04"4# 2[06"4# 2[10"5# 2[20"4#

0 Sb 0 Zr0 1 Zr1

2[27"5# 2[30"4# 2[41"4#

Zr2

0 H6 0 H2 0 H2 0 H4

0[77"00# 0[84"6# 0[88"7# 1[90"8#

0 H3 0 Zr0 0 Sb 0 Sb

1[13"7# 1[60"4# 1[76"09# 1[86"8#

0 Sb 0 Zr0 1 Zr2 0 Zr1

2[99"8# 2[91"4# 2[94"4# 2[09"4#

0 Zr1 0 Zr1

2[06"4# 2[20"4#

Sb

0 H2 0 H7 0 H3 0 H2

1[96"01# 1[98"02# 1[12"8# 1[16"01#

0 H6 0 H4 0 Zr2 0 Zr1

1[23"09# 1[28"8# 1[76"09# 1[85"6#

0 Zr2 0 Zr0 0 Zr2 0 Zr0

1[86"8# 2[99"6# 2[99"8# 2[90"6#

0 Zr1 0 Zr1 0 Zr1

2[96"5# 2[10"5# 2[27"5#

H0 H1 H2

3 Zr1 3 Zr0 0 Zr2 0 Zr2 0 Zr1 0 Zr1 0 Zr1 0 Zr1 0 Zr1

1[95"2# 0[65"3# 0[84"6# 0[88"7# 0[68"6# 0[81"5# 0[74"7# 0[67"8# 0[60"06#

0 Sb

1[96"01#

0 Sb

1[16"01#

0 Zr0

1[21"6#

0 Zr1 0 Zr0 0 Zr0 1 Zr0 0 Sb

0[84"6# 0[84"7# 1[30"7# 0[77"7# 1[98"02#

0 Zr2 0 Zr2 0 Zr1 0 Sb 0 Zr0

1[13"7# 1[90"8# 1[26"7# 1[23"09# 1[0"0#

0 Sb 0 Zr0 0 Zr2 0 Zr2 0 Zr0

1[12"8# 1[94"6# 1[31"7# 1[26"8# 1[0"1#

H3 H4 H5 H6 H7

0 H1 0 H6 0 H4 0 H4

 Zr1  "Zr\Fe#

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Fig[ 2[ Fragment of the Zr4FeSb1H00[2 structure[

Fig[ 3[ X!ray di}raction patterns of Zr5NiAl1 before "a# and after "b# hydrogenation "deuterium#[ The stars show the Si re~ections used for calibration[

Zr5Fe0[4Sn0[4 compounds leads to a change of the initial crystal structure from the Fe1P type to the Ni2P one[ The main phase of the hydrogenated samples Zr5Co0[4Sn0[4Hx and Zr5Ni0[4Sn0[4Hx is the phase of the Fe1P type but a little amount of the Zr4Sn2 hydride and unknown phase

were found as well[ The hydrogen uptakes determined by weighing the samples are respectively close to 00 and 09 for the Co and Ni compounds\ accounting that H is included also into other minor phases[ Besides\ we can estimate approximately the number of absorbed hydro!

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Table 3 Results of the re_nement of neutron powder di}raction data for Zr5NiAl1D6[4

Table 5 Results of the re_nement of neutron powder di}raction data for Zr5NiAl1H8[5

Atom

Site

x:a

y:b

z:c

Atom

Site

x:a

y:b

z:c

Zr0 Zr1 Ni Al D0 D1 D2 D3

5h 5` 1b 3f 1a 5h 5h 5`

9[489"1# 9[1328"09# 9 0:2 9 9[103"2# 9[334"1# 9[180"1#

−9[9428"03# 9 9 1:2 9 9[039"1# 9[0272"03# 9

0:3 9 0:3 9[433"1# 0:1 0:3 2:3 0:1

Zr0 Zr1 Ni Al H0 H1 H2 H3 H4

5h 5` 1b 3f 1a 5h 5h 5` 01i

9[466"1# 9[158"1# 9 0:2 9 9[253"6# 9[322"03# 9[158"2# 9[476"00#

−9[946"1# 9 9 1:2 9 9[000"3# 9[025"09# 9 9[980"00#

0:3 9 0:3 9[448"6# 0:1 2:3 0:3 0:1 9[395"09#

B"is:eq#  0[2"0#[ Occupations] D3\ 9[54"0#D^ D1\ 9[70"1#D^ D2\ 9[69"0#D[ RI  9[9584\ RP  9[9878[

gen atoms from the comparison of the cell volumes of di}erent compounds\ assuming that the relative increase of the cell volume is proportional to this number[ The respective cell volumes of the Zr5Co0[4Sn0[4 and Zr5Ni0[4Sn0[4 hydrides are 100[0 and 198[0 _2 and ref! erence to the volume expansion of the parent system Zr5NiAl1ÐZr5NiAl1H8[5 "see below#\ the x values are esti! mates to 09[0 and 09[4 for the Co and Ni compounds respectively "Table 0#[ These values agree well with those found before[ Zr5NiAl1 Finally\ we have studied two Zr5NiAl1 samples charged with hydrogen "as previously done# and deuterium "low pressure and temperature of activation#\ respectively[ The X!ray pattern of Zr5NiAl1 and Zr5NiAl1D6[4 are shown in Fig[ 3[ The crystal structure was derived from neutron

B"is:eq#  9[7"0#[ Occupations] H1\ 9[67"6#H^ H2\ 9[32"6#H^ H4\ 9[22"3#H[ RI  9[9518\ RP  9[9583[

di}raction data and the results are listed in Tables 3 and 5[ The observed\ calculated and di}erence neutron patterns are shown in Fig[ 4a\ 4b[ The Zr5NiAl1D6[4 hydride crystallizes with the Zr5FeAl1D09 type\ the deuterium atoms occupy similar sites as already found in Zr5FeAl1D09\ however three sites are not completely occupied "Table 3#[ The D coor! dination polyhedra and the interatomic distances "Table 4# are found similar for that of Zr5MAl1D09[ The Zr5NiAl1H8[5 hydride is more charged than the parent deuteride[ Besides the similar sites as already found in Zr5NiAl1D6[4\ the H atoms partly occupy the 01i site with a ratio of 9[22[ The interatomic distances for Zr5NiAl1H8[5 are listed in Table 6[ It is noteworthy that a high thermal stability is found for Zr4FeSb1H00[2[ Heating a Zr4FeSb1H00[2 sample under

Table 4 Selected interatomic distances "_# for Zr5NiAl1D6[4 Zr0

0 D1 0 D2 1 D3

0[89"2# 0[82"1# 0[868"09#

0 D2 1 Al 1 Zr1

1[94"1# 2[928"03# 2[973"00#

0 Ni 1 Al

2[025"03# 2[131"01#

1 Zr1 1 Zr1

2[379"00# 2[433"01#

Zr1

0[871"7# 1[19"1# 1[192"02# 0[42"1#

1 D2 1 Ni 1 Zr0 1 D2

1[296"09# 1[562"5# 2[973"8# 0[683"0#

1 Al 1 Zr1 1 Zr0 5 Zr1

2[042"5# 2[322"6# 2[379"09# 1[562"0#

1 Zr0 1 Zr1

2[433"03# 2[476"0#

Ni

0 D0 1 D3 1 D1 2 D1

2 Zr0

2[025"01#

Al

0 Al

1[84"1#

2 Zr0

2[928"03#

2 Zr1

2[042"1#

1 Zr0

2[131"02#

D0 D1 D2 D3

1 Ni 0 Ni 0 Zr0 0 Zr0

0[683"0# 0[42"1# 0[82"1# 0[868"7#

2 Zr1 0 Zr0 0 Zr0 0 Zr0

0[871"0# 0[89"1# 1[94"1# 0[868"09#

1 Zr1 1 Zr1 0 Zr1

1[192"01# 1[296"8# 1[19"1#

0 Zr1

1[19"1#

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Fig[ 4[ Observed "dots#\ calculated "line# and di}erence neutron di}raction patterns of Zr5NiAl1D6[4 "a# and Zr5NiAl1H8[5 "b#[

894

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normal hydrogen pressure during 13 h at 399>C\ only provokes a small increase of the cell parameters[ Some weak Bragg lines of another type of compound appear not belonging to Zr hydrogen systems "Fig[ 5#[ The drastic change of the crystal structure upon hydro! genation is rather unusual[ As said before\ some modi! _cations of the structure have been already reported in the Fe1P type of compounds*double c cell parameter for Zr5FeAl1D09 or orthorhombic distortion of RNiAL[ Therefore\ these remain rather limited changes of the crystal structure[ According to Krypiakevych|s classi! _cation ð03Ł\ the Fe1P and the Ni2P types belong to di}er! ent classes\ the _rst one is related with the class having a trigonal coordination of the smallest atom whereas the Ni2P type of structure exhibit a tetragonalÐantiprismatic coordination of the smallest atom[ We think that the structure transformation results in the supersaturating by hydrogen "deuterium# of the Fe1P type compounds[ Bearing in mind that ZrNiAl absorbs up to 9[2 hydrogen atoms\ we _rst assume that in parent Zr compounds the number of absorbed hydrogen is roughly proportional to the Zr content per fu[ This does not explain why Zr5NiAl1 absorbs relatively six times more hydrogen than ZrNiAl[ In the deuterated com! pound the D atoms are not inserted into polyhedra with Al close neighbours[ More severe conditions of hydro! genation "high temperature and pressure# made easy the insertion of H"D# into polyhedra with top X atoms "e[g[

Zr5NiAl1H8[5#[ Antimony which is relatively more elec! tronegative and larger size than Al makes the Fe1P H! rich quaternary unstable\ in such a way that a structure transformation occurs[ The stability of the Ni2P structure having a large Zr content is con_rmed when X  Sb with Zr2Sb[ Tin\ which has intermediate characteristics\ forms di}erent Fe1P type compounds characterized by a com! petition between two states[ A structure transformation occurs during hydrogenation of Fe compound but others "with Co\ Ni# are not transformed[

3[ Conclusion New complex hydrides of Zr rich with Fe\ Co\ Ni and Sb "Al\ Sn# alloys have been synthesized[ Their crystal structure was studied using powder neutron di}raction[ Zr rich tetrahedra and trigonal bipyramids are occupied by hydrogen up to a total H:M ratio of about 0[22[ The most unexpected feature is a crystal structure trans! formation upon hydrogen insertion from a Fe1P type metal matrix to a Ni2P type quaternary hydride[ The change of structure is observed with the largest and most electronegative X  Sb\ reference to Al\ and for the inter! mediate X  Sn the transformation is not systematic[ At present\ works are in progress to investigate the kinetics of hydrogenation and dehydrogenation in detail\ as well as the thermal and hydrogen pressure stability[

Fig[ 5[ X!ray di}raction patterns of Zr4FeSb1H00[2 sample before "a# and after "b# heating at 399>C for 13 h[ The stars show the Si re~ections used for calibration[

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Acknowledgements R[V[ Skolozdra would like to thank the French Min! istry of National Education and Research and the CNRS for providing a renewed position as Invited Professor at the University Joseph Fourier*Grenoble I[ References ð0Ł Villars P\ Calvert LD[ Pearson|s handbook of crys! tallographic data for intermetallic phases\ vol[I[ American Soc for Metals\ Metals Park 0874[ p[ 448Ð59[ ð1Ł Krypyakevich PI\ Markiv VYa\ Melnyk EV\ Dopov Akad Nauk Ukr SSR 0856^7"A#]649[ ð2Ł Yoshida M\ Akiba E\ Shimojo Y\ Morii Y\ Izumi F[ J[ Alloys + Compounds 0884^120]644[ ð3Ł Kolomiets AV\ Havela L\ Yartys VA\ Andreev AV[ J[ Alloys + Compounds 0886^142Ð143]232[ ð4Ł Kolomiets AV\ Havela L\ Andreev AV\ Sechovsky V\ Yar! tys VA[ J[ Alloys + Compounds 0886^151Ð152]195[ ð5Ł Burnashova VV\ Markiv VYa[ Dopov Akad Nauk Ukr SSR 0858^3"A#]240[

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ð6Ł Krypyakevich PI\ Burnashova VV\ Markiv VYa[ Dopov Akad Nauk Ukr SSR 0869^8"A#]717[ ð7Ł Gingl F\ Yvon K\ Zavaliy IYu\ Yartys VA\ Ficher P[ J[ Alloys + Compounds 0884^115]0Ð3[ ð8Ł Melnyk GA\ Fruchart D\ Romaka LP\ Stadnyk JuV\ Sko! lozdra RV\ Tobola J[ J[ Alloys + Compounds 0887^156]L0Ð 2[ ð09Ł Stadnyk YV\ Romaka LP\ Pecharski VK\ Skolozdra RV[ Neorganischeskie Materialy 0884^18]14[ ð00Ł Zavaliy IYu[ In] The peculiarities of synthesis and crystal structure of hydrides of some intermetallic compounds in ZrÐMÐX systems "M*d!metal\ X*p!element#[ ICHMS! 86\ Abstracts\ Katsively "Ukraine# 0886[ p[ 28[ ð01Ł Zavaliy IYu\ Pecharsky V\ Kopylets V\ Akselrud L[ Hydro! genation of Zr5MX1 compounds "M  FE\Co\Ni\ X  Al! \Ga\Sn#] precise study of the crystal structure and band structure calculations[ In] MRS 0887 Spring Meeting\ Abstracts\ San Francisco H7[16\ 0887[ ð02Ł Akselrud LG\ Gryn|Yu N\ Zavaliy PYu\ Pecharsky VK[ CSD!universal program package for single crystal and:or powder structure data treatment[ In] 01\ European Crys! tallogr Meeting\ Abstracts\ Moscow\ vol[ 2\ 0878[ p[ 044[ ð03Ł Krypyakevich PI[ Structure types of intermetallic compounds[ Nauka\ Moscow] 0866[ p[ 0Ð117[