Samples Consist Of Major 1212 Phase Biology Essay
Powder X-ray diffraction analyses revealed all samples consist of major 1212 stage with tetragonal unit cell ( infinite group P4/mmm ) , and minor 1201 stage and little sum of other drosss. Table 4.1 lists the values of 1212:1201 stage ratio and 1212 lattice parametric quantities for Tl0.85Cr0.
15Sr2CaCu2-xGexO7-I? ( x= 0, 0.1, 0.2, 0.
3, 0.4, 0.6 ) samples. The extremums due to the 1201 stage and GeO2 dross are marked with a * and # severally.
These 1212:1201 stage ratios was calculated from the diffraction strengths of 1212, 1201 and other stages ( drosss ) by utilizing the equations 3.11 and 3.12. The 1212 vol. % was good above 80 % for x= 0-0.3, whereas for x= 0.
4 and 0.6, the per centum dropped to 72 % and 60 % severally ( Table 4.1 ) . The dropped of 1212 vol. % below 70 % was mostly due to much higher sum of 1201 stage and presence of GeO2 and other drosss. The XRD information showed a lessening of c-lattice parametric quantity with Ge content increase.
But, there is no important alteration in the a-lattice parametric quantity. This suggests possible Ge4+ ( 53 autopsy ) is much smaller than the ionic radius of Cu2+ ( 73 autopsy ) . It is suggested that, the permutation of Ge for Cu can be an effectual manner to stabilise 1212 stage formation [ Shukor & A ; Arulsamy, 2000 ] .Figures 4.7-4.12 show the electrical electric resistance of Tl0.85Cr0.
15Sr2CaCu2-xGexO7-I? ( x= 0-0.6 ) . The consequences show a rebuff increased in Tc nothing was observed for the Tl0.85Cr0.15Sr2CaCu2-xGexO7-I? , x=0.
1 sample ( 100 K ) compared to the free Ge compound ( 98 K ) . The Tc oncoming and Tc zero for x= 0.2 and 0.
3 samples were observed above 90 K and 80 K severally. However, for sample x= 0.4 the Tc oncoming dropped to 66.3 K ( Table 4.
2 ) . The x=0-0.3 samples ( Figs.
4.7-4.10 ) showed metallic normal province behaviour. Further permutation of Ge caused the normal province to alter from metallic-semimetallic behaviour at x=0.4 ( Fig. 4.11 ) and insulating behaviour at x=0.6 ( Fig.
4.12 ) . Based on ascertained Tc oncoming values and consequences of XRD of the samples which showed dominant 1212 stage, it is suggested that the 1212 stage is responsible for the ascertained superconductivity of the x=0-0.3 samples and non the minor 1201 stage as the Tc oncoming for the latter has been reported to be below 50 K [ Sheng et al. , 1991 ] . The lessening in Tc nothing for x a‰? 0.
2 samples can be attributed to the increasing sum of 1201 superconducting stage and GeO2 within the 1212 superconducting matrix, as shown in Table 4.1. It was suggested that the alterations in normal province behaviour and depression of Tc zero ( Table 4.2 ) , with increase of GeO2 ( Figs. 4.1-4.6 ) are related to the decrease of the charge bearer concentration.Simple valency computation indicates that Tl0.
85Cr0.15Sr2CaCu2O7-I? is somewhat overdoped with hole bearers and permutation of the higher valency Ge4+ reduced mean Cu valency in the CuO2 planes and caused hole concentration to diminish [ Subramaniam et al. , 1998 ; Shukor & A ; Arulsamy, 2000 ; Hamid et al. , 2004 ] .
The optimal hole concentration was suggested at x= 0.1, as the sample showed highest Technetium zero amongst samples. Further permutation of Ge4+ was expected to diminish holes concentration below the optimal concentration and caused Tc nothing to bead. However, intriguingly, Table 4.2 showed that at x= 0.2-0.3 samples, the bead in Tc nothing was slow and the values are still maintained above 80 K. Thus, the possible ground for this behaviour is given in the visible radiation of our treatment on the fluctuation induced conduction and FTIR analyses below.
The Micrographs of Tl0.85Cr0.15Sr2CaCu2-xGexO7-I? samples are shown in Figures 4.13-4.18. The micrographs were taken at 3000X magnifications of the fractured internal subdivisions of the samples. The micrographs revealed porous microstructure with grains that are of irregular forms and of around 1-3 I?m in sizes. No important alterations in microstructure were observed for x= 0.
1-0.4 samples as compared to the microstructure of the x= 0 sample. The micrograph of x= 0.6 sample shows unclear grains morphology.Probe on the superconducting fluctuation behaviour of Tl0.85Cr0.15Sr2CaCu2-xGexO7-I? series by extra conduction analyses utilizing the AL and LD theories were carried out. Figs.
4.19- 4.22 shows the temperature dependance of electrical electric resistance with normal province behaviour fitted to the additive relation I?= a+bT for x=0-0.3. The extra conduction ( a?†I? ) was determined by detecting the divergence of electric resistance, I? ( T ) from this background electric resistance of one-dimensionality line. The inset in Figs. 4.19-4.
22 show the curves of the temperature dependance of the derived function of electric resistance where the peak temperature, Tcp was used to cipher decreased temperature, Iµ . In order to compare experimental informations with the AL theory for the fluctuation conduction, ln ( a?†I?/I?0 ) versus ln Iµ was plotted in Figs. 4.23-4.26. The figure shows the fluctuation conduction for all samples covering the average field government, -5 & lt ; ln Iµ & lt ; -2.
Table 4.3 listed critical advocate, I»2D, I»3D, 2D-3D passage temperature, T2D-3D value for Tl0.85Cr0.15Sr2CaCu2-xGexO7-I? . From critical advocate value ( I» ) , the conducting channel dimension can be determined. For pure samples merely 2D carry oning channel was observed. As Ge4+ was substituted into the superconducting sample, the passage from 2D to 3D behaviour was observed as temperature was reduced.
Table 4.4 shows calculated values of I?c ( 0 ) , J and I? of all samples for Tl0.85Cr0.15Sr2CaCu2-xGexO7. Substitution of Ge at Tl1212 compound caused I?c ( 0 ) to diminish from 0.26A ( x= 0.1 ) to 0.19 A ( x= 0.
2 ) , before increasing back to its highest value of 0.29 A ( x= 0.3 ) .
The highest value of J was found at x= 0.3 which besides recorded the lowest anisotropy, I? value ( Table 4.4 ) .The 2D fluctuation behaviour that are observed for the un-substituted Tl0.85Cr0.15Sr2CaCu2O7 sample ( Fig. 4.
23 ) is in contrast to the extra conduction analyses of the Ge permutation samples which indicate 2D to 3D passages in the normal province ( Figs. 4.24-4.26 ) and besides from old studies on Y123 [ Sudhakar et Al, 1991, Upreti et al. , 1996 ] , ( Cu, Tl ) -based [ Nawazish A Khan & A ; Irfan, 2008 ; Khan & A ; Husnain, 2006 ; Khan et Al, 2003 ] , Cu-substituted Tl1-xCuxSr1.2Yb0.8CaCu2O7-I? , Tl1-xCuxSr1.6Yb0.
4CaCu2O7-I? [ Huda & A ; Yahya, 2009 ; Ahmad et al. , 2009 ] and Yb-substituted Tl0.5Pb0.5Sr2-xYbxCaCu2O7-I? [ Huda et al.
, 2008 ] superconductors which showed 2D to 3D passage behaviours. The 2D to 3D passage in the normal province is suggested to be induced by partial permutation of Ge4+ into CuO2 planes. The deliberate I?c ( 0 ) values for Tl0.85Cr0.15Sr2CaCu2-xGexO7-I? ( Table 4.4 ) are comparable to the lower value in the scope of 0.03-0.
68 nanometer reported for dual layer Tl-based compounds [ Gernot Krabbes et al. , 2006, Safa O. Kasap & A ; Peter Capper, 2006 ] . The little I?c ( 0 ) values indicate high grade of anisotropy for the Tl1212 samples.In analysing the bond lengths of the superconducting samples, the FTIR measurings were carried out.
Fig. 4.27 shows consequences of FTIR soaking up measurings of Tl0.85Cr0.15Sr2CaCu2-xGexO7-I? ( x=0.1, 0.2, 0.
3, 0.6 ) superconductors. For the un-substituted x=0 sample, the apical O manner of the type Cu ( 2 ) -O ( 2 ) -Cr is peaked around 534cm-1, Cu ( 2 ) -O ( 2 ) -Tl around 400-480cm-1 and CuO2 planar O manner around 586cm-1. The peak strength of Cu ( 2 ) -O ( 2 ) -Cr decreases whereas and that of Cu ( 2 ) -O ( 2 ) -Tl manner increases with increased Ge permutation. In Ge substituted Tl0.85Cr0.
15Sr2Ca1 ( Cu2-xGex ) O7-d ( x=0.1, 0.2, 0.3, 0.6 ) the apical O manners of type Ge/Cu ( 2 ) -O ( 2 ) -Cr are observed around 556, 549, 553, 553cm-1 and Ge/Cu ( 2 ) -O ( 2 ) -Tl manner around 472, 470, 473, 471cm-1. The CuO2/GeO2 planar manners are observed around 589, 588, 573, 565cm-1 for Ge-doping of x=0.
1, 0.2, 0.3, 0.6.
These observations have shown that Ge/Cu ( 2 ) -O ( 2 ) -Cr apical O manner is hardened compared to the x= 0 sample whereas the Ge/Cu ( 2 ) -O ( 2 ) -Tl is softened with increased Ge permutation. In add-on, the GeO2/CuO2 planar manner is softened in the Ge-substituted samples with higher Ge.The hardening of Ge/Cu ( 2 ) -O ( 2 ) -Cr manner and at the same time softening of Ge/Cu ( 2 ) -O ( 2 ) -Tl manner ( Fig. 4.
27 ) seems to advance tilting of bonds of the CuO2 planes, which in bend consequences in the softening of CuO2 planar manner. However, based on the ratio of Tl to Cr in the composing, it is suggested that softening of Ge/Cu ( 2 ) -O ( 2 ) -Tl manner dominated in these samples. Observation of lessening in peak strength of Ge/Cu ( 2 ) -O ( 2 ) -Cr and addition in Ge/Cu ( 2 ) -O ( 2 ) -Tl strength with Ge permutation besides farther enhanced the suggestion ( Fig. 4.27 ) . Additionally, softening of the Ge/Cu ( 2 ) -O ( 2 ) -Tl apical O manners indicates increasing distance between Tl-O and CuO2 planes in concurrence with XRD consequences which showed lessening in c-axis length with Ge content ( Table 4.1 ) , suggest that the CuO2/GeO2 interplanar distance is reduced with Ge permutation.
The decrease caused increased CuO2/GeO2 matching which in bend lead to an addition in the denseness of bearers and resulted in enhanced Fermi vector, kF ( = ( 3Iˆ2N/V ) 1/3 ) , coherency length along c-axis I?c ( = N›2kF/2ma?† ) and besides Fermi speed VF ( = N›kF/m ) [ Tinkham, 1996 ; Ihara et al. , 1999 ] . This suggestion is supported by the computation utilizing the Lawrence-Doniach theoretical account which revealed the highest superconducting coherency length, I?c ( 0 ) and interplanar yoke, J at x=0.3 ( Table 4.4 ) .
The increased coherency length along the c-axis promotes a lessening in anisotropy, I? ( Table 4.4 ) which may explicate sustainability of superconducting behaviour with Tc zero above 80 K at x= 0.2-0.3 mentioned earlier [ Ihara et al. , 1999 ; Ihara et al. , 2000 ] .
On the other manus, the crisp lessening in Tc nothing for x a‰? 0.4 is likely due to the much reduced holes concentration as a consequence of the high concentration of Ge.5.2 Tl0.85Cr0.15Sr2-yGeyCaCu2O7-I? ( y= 0.
03, 0.05, 0.08, 0.10, 0.15, 0.20, 0.
30, and 0.40 ) SeriesPowder X-ray diffraction analyses ( Figs. 4.28 – 4.35 ) revealed all samples consist of major 1212 stage with tetragonal unit cell ( infinite group P4/mmm ) accompanied by minor 1201 stage. The 1212:1201 stage ratio and 1212 lattice parametric quantities for all samples are shown in Table 4.5.
The 1212 volume by and large increased with Ge content up to y= 0.08 and decreased for y & gt ; 0.08. However, in general, the 1212 volume was above 84 % for y= 0 to y= 0.15, whereas for y= 0.2 and 0.3, the per centum dropped due to the rise of the 1201 stage and other drosss. The c-lattice parametric quantity from the XRD measurings showed diminishing value as Ge content was increased.
Figures 4.36-4.43 showed the electrical electric resistance of Tl0.85Cr0.
15Sr2-yGeyCaCu2O7-I? ( y= 0-0.30 ) samples. The y= 0-0.15 samples showed metallic normal-state behaviour with Tc zero above 88 K ( Table 4.6 ) but as Ge content was further increased, Tc zero dropped to below 80 K with the normal-state behaviour of the electric resistance curve showed semi-metallic behaviour at y= 0.20 and insulating behaviour at y= 0.30. Based on the ascertained Tc oncoming values ( Table 4.
6 ) it is suggested that superconductivity of the y= 0-0.3 samples is dominated by the Tl1212 stage and non the minor 1201 stage as Tc oncoming for the latter has been reported to be below 50 K [ Sheng et al. , 1991 ] .The influence of Ge4+ permutation at the Sr-site on bearer concentration is indicated by the transmutation of the normal province from metallic ( y=0-0.15 ) to semi-metallic ( y=0.2 ) and to insulator ( y=0.3 ) behaviour with Ge4+ content ( Table 4.6 ) .
The alterations point toward gradual shifting of the doping degree to an under-doped province. The free Ge compound ( Tl0.85Cr0.15 ) Sr2CaCu2O7 is somewhat overdoped with hole bearers [ Sheng et al. , 1991 ] and permutation of higher valency Ge4+ to the superconductor sample caused lessening in hole concentration. For Tl1212, the optimal Cu valency was suggested at 2.33 [ Shukor & A ; Arulsamy, 2000 ; Hamid et Al, 2004 ] .
Further Ge permutation leads to underdoping and normally degrades Tc [ Nkum & A ; Datars, 1992 ; Khan & A ; Irfan, 2008 ] . The addition in 1212 volume with Ge for y= 0-0.08 and the lessening for Y & gt ; 0.08 may be related to the optimal Cu valency. As hole concentration attack the optimal Cu valency value, 1212 stage volume increased, but beyond 2.33, 1212 stage volume decreased.
However, intriguingly, for y= 0-0.15, non merely the normal province behaviour remained metallic, Tc zero was maintained above 87 K before bit by bit suppressed for Y & gt ; 0.15 ( Table 4.6 ) .The micrographs of Tl0.85Cr0.15Sr2-yGeyCaCu2O7-I? samples showed microstructures of indiscriminately oriented plate-like grains of about 4-6 Aµm in grain sizes for y= 0.
03-0.15 ( Figs. 4.44-4.51 ) .
This in contrast to the micrographs of y= 0.2 – 0.4 samples which showed non-homogeneous guerrilla shaped grains morphology. It is interesting to observe that the normal province behaviour of the y= 0.03-0.15 samples to be metallic as opposed to the y= 0.2 sample which is semimetallic and the y= 0.
3 and 0.4 samples which are insulating. Therefore, the consequences indicate some microstructure influences on the superconducting behaviour of the samples.The extra conduction analyses of Tl0.85Cr0.15Sr2-yGeyCaCu2O7-I? series utilizing the AL and LD theoretical accounts were carried out. Figs. 4.
52-4.56 show the temperature dependance of electrical electric resistance with normal province behaviour fitted to the additive relation I?= I±+I?T for samples y= 0-0.15. The extra conduction ( a?†I? ) was determined by detecting the divergence of electric resistance curve, I? ( T ) from this fitted of additive line. The inset in Figs. 4.
52-4.56 show the curves of the temperature dependance of the derived function of electric resistance where the peak temperature, Tcp was used to cipher decreased temperature, Iµ . The graph of ln ( a?†I?/I?0 ) versus ln Iµ was plotted for samples y= 0-0.15, which showed metallic normal province behaviour ( Figs.
4.57-4.61 ) . The curves derived from experimental informations were so compared against the computed curves based on the AL equation ( Eq. 3.15 ) . For the un-substituted sample, the comparing yielded a 2D fluctuation behaviour but as Ge4+ permutation was increased a passage from 2D to 3D behaviour was observed with decrease in temperature. The highest ascertained T2D-3D was 99.
6 K for y=0.10 ( Table 4.7 ) . Interestingly, the permutation of Ge into Tl0.
85Cr0.15Sr2-yGeyCaCu2O7-I? was able to bring on 2D to 3D passage even at really low Ge content of y= 0.03 ( Table 4.7 ) . This confirms strong influence of Ge permutation on the superconducting fluctuation behaviour, SFB of Tl1212. Previous surveies on Tl1-xCuxSr1.2Yb0.8CaCu2O7-I? [ Huda & A ; Yahya, 2009 ] , Tl1-xCuxSr1.
6Yb0.4CaCu2O7-I? [ Ahmad et al. , 2010 ] and Tl0.5Pb0.5Sr2-xYbxCaCu2O7-I? [ Huda et al. , 2008 ] besides showed the similar influence of elemental permutations on SFB and 2D to 3D passage.By utilizing the Lawrence Doniach equations, the values of I?c ( 0 ) , J, I? were determined for all samples and tabulated in Table 4.
8. The values of I?c ( 0 ) for y=0.08 showed the largest coherency length of 0.47 A amongst the samples. The y= 0.08 sample besides showed the highest value of J ( 0.087 ) and the lowest value of anisotropy, I? .
The consequences indicate that Ge permutation can bring on modify I?c ( 0 ) which in bend addition interlayer matching strength and cut down anisotropy of the sample. The deliberate values of I?c utilizing the Lawrence Doniach theory, in the present work ( Table 4.8 ) , are comparable with the reported I?c of dual layer Tl-based compound which was in the scope of 0.
3-6.8 A [ Gernot Krabbes et al. , 2006, Safa O. Kasap & A ; Peter Capper, 2006 ] .FTIR consequence for Tl0.
85Cr0.15 ( Sr2-yGey ) CaCu2O7 is shown in Figure 4.62.
In the un-doped Tl0.85Cr0.15Sr2CaCu2O7 ( free Ge ) sample, the apical O manners in the signifier of wide sets of types Cu ( 2 ) -O ( 2 ) -Tl and Cu ( 2 ) -O ( 2 ) -Tl/Cr are observed between 400-550cm-1 [ Ahmad et Al, 2010 ; Kulkarni et Al, 1990 ; Khan & A ; Husnain, 2006 ] . A wide Cu ( 2 ) -O ( 2 ) -Tl manner is observed in the moving ridge figure scope 420-480cm-1 [ Ahmad et Al, 2010 ; Kulkarni et Al, 1990 ; Khan & A ; Husnain, 2006 ] which somewhat increases in strength with increased Ge doping. The Cu ( 2 ) -O ( 2 ) -Cr/Tl manner [ Ahmad et Al, 2010 ; Kulkarni et Al, 1990 ; Khan & A ; Husnain, 2006 ] , nevertheless, is softened with increased Ge doping and is observed around 552, 552, 552, 549.3, 548.2, 548, 548, 548cm-1 in Tl0.
85Cr0.15 ( Sr2-yGey ) CaCu2O7 ( y=0.05, 0.08, 0.10, 0.15, 0.20, 0.
30, 0.40 ) samples. In Tl0.85Cr0.15 ( Sr2-yGey ) CaCu2O7 samples doped with little Ge concentration ( y=0.03 ) , the CuO2 planar O manner is observed around 571cm-1 [ Ahmad et Al, 2010 ; Kulkarni et Al, 1990 ; Khan & A ; Husnain, 2006 ] . This manner in Tl0.
85Cr0.15 ( Sr2-yGey ) CaCu2O7 ( y=0.05, 0.08, 0.10, 0.15, 0.20, 0.30, 0.
40 ) samples is observed around 571, 573, 573.6, 573.6, 573.6, 578.4, 581.6cm-1, Fig.
4.62.The hardening of planar O manners with increased Ge doping is most likely due to electronegativity of Ge. The electronegativity of Ge ( 1.8 Pauling ) is much higher than that of Sr atoms ( 1.0 Pauling ) . It is possible that the doped Ge+4 atoms with higher electronegativity and smaller ionic radius would exercise more attractive interaction of the apical O atom to Ge atoms which will heighten their bending towards them.
The bending of apical O atoms towards Ge+4 atoms would cut down attractive interaction between Ge+4 and CuO2 planar O atoms and accordingly would diminish planar bending/tilting which perchance consequences into hardening of CuO2 planar O with increased Ge doping. In add-on, the bending of apical O manners toward Ge resulted in softening of these apical O manners. However, XRD consequences which showed lessening in c-axis length ( Table 4.5 ) as a consequence of Ge permutation, indicates possible lessening in separation distance between CuO2 planes. The lessening separation distance between planes would ensue in addition in denseness of charge bearer ( N/V ) and therefore connote addition in Fermi vector, kF ( = ( 3Iˆ2N/V ) 1/3 ) and c-axis coherency length, I?c ( = N›2kF/2ma?† ) [ Tinkham, 1996 ; Ihara et Al, 1999 ] .
The sweetening of CuO2 planes matching is suggested to heighten superconducting belongingss of the compounds and nutriment of Tc zero above 89 K ( Table 4.6 ) for x= 0.03-0.15 [ Tinkham, 1996 ; Ihara et Al, 1999 ] .