“…This result may suggest a complex arrangement of chromium, copper, and oxygen in the (Cu,Cr) plane. 59,61,62 The T c presents a variation from complete suppression at n ) 1 via the maximum of 103 K at n ) 3, then to complete suppression again for n g 8 (Figure 7). It is believed that this variation reflects the variation of the hole concentration; that is, the system changes from an overdoped region of holes for n e 2 to an underdoped region for n g 4 through the optimum point at n ) 3.…”
Section: Homologous Series Of Superconductors Stable Under High Pressurementioning
confidence: 96%
“…As is shown in Figure , the a -parameter of the chromium system is larger than this value for the entire range of n despite a relatively small ionic radius of the hexavalent chromium. This result may suggest a complex arrangement of chromium, copper, and oxygen in the (Cu,Cr) plane. ,, 7 Variation of the a -parameter, T c and the optimum excess oxygen content δ in starting mixture for (Cu,Cr)-12( n -1) n -Sr …”
Section: Homologous Series Of Superconductors
Stable Under High Pressurementioning
confidence: 96%
“…Chromium has been known as an effective charge reservoir substituent for mercury in the Hg-12( n -1) n -A (A = Sr, Ba) family, − its oxycarbonate derivatives or thallium for the Tl-12( n -1) n -A family, − and its oxycarbonates . According to neutron diffraction studies for some of these phases, ,, chromium adopts tetrahedral coordination, forming a CrO 4 group.…”
Section: Homologous Series Of Superconductors
Stable Under High Pressurementioning
confidence: 99%
“…Chromium has been known as an effective charge reservoir substituent for mercury in the Hg-12( n -1) n -A (A = Sr, Ba) family, − its oxycarbonate derivatives or thallium for the Tl-12( n -1) n -A family, − and its oxycarbonates . According to neutron diffraction studies for some of these phases, ,, chromium adopts tetrahedral coordination, forming a CrO 4 group. This result implies that chromium has a hexavalent state in an oxide superconductor because trivalent chromium prefers strongly octahedral coordination because of its large crystal field stabilization energy in an octahedral site.…”
Section: Homologous Series Of Superconductors
Stable Under High Pressurementioning
Under high pressure, a variety of elements can be accommodated at the cation sites in
the charge reservoirs of cuprate superconductors. Furthermore, high pressure allows the
insertion of higher number of CuO2 planes (i.e., the insertion period of a charge reservoir
becomes variable). Because of these effects, many new high critical temperature (T
c)
superconductors have been discovered under high pressure. In this paper, we will survey
their structural and superconducting properties. The role of high pressure and its effect on
the size mismatch between the charge reservoir and the CuO2 plane will also be discussed.
“…This result may suggest a complex arrangement of chromium, copper, and oxygen in the (Cu,Cr) plane. 59,61,62 The T c presents a variation from complete suppression at n ) 1 via the maximum of 103 K at n ) 3, then to complete suppression again for n g 8 (Figure 7). It is believed that this variation reflects the variation of the hole concentration; that is, the system changes from an overdoped region of holes for n e 2 to an underdoped region for n g 4 through the optimum point at n ) 3.…”
Section: Homologous Series Of Superconductors Stable Under High Pressurementioning
confidence: 96%
“…As is shown in Figure , the a -parameter of the chromium system is larger than this value for the entire range of n despite a relatively small ionic radius of the hexavalent chromium. This result may suggest a complex arrangement of chromium, copper, and oxygen in the (Cu,Cr) plane. ,, 7 Variation of the a -parameter, T c and the optimum excess oxygen content δ in starting mixture for (Cu,Cr)-12( n -1) n -Sr …”
Section: Homologous Series Of Superconductors
Stable Under High Pressurementioning
confidence: 96%
“…Chromium has been known as an effective charge reservoir substituent for mercury in the Hg-12( n -1) n -A (A = Sr, Ba) family, − its oxycarbonate derivatives or thallium for the Tl-12( n -1) n -A family, − and its oxycarbonates . According to neutron diffraction studies for some of these phases, ,, chromium adopts tetrahedral coordination, forming a CrO 4 group.…”
Section: Homologous Series Of Superconductors
Stable Under High Pressurementioning
confidence: 99%
“…Chromium has been known as an effective charge reservoir substituent for mercury in the Hg-12( n -1) n -A (A = Sr, Ba) family, − its oxycarbonate derivatives or thallium for the Tl-12( n -1) n -A family, − and its oxycarbonates . According to neutron diffraction studies for some of these phases, ,, chromium adopts tetrahedral coordination, forming a CrO 4 group. This result implies that chromium has a hexavalent state in an oxide superconductor because trivalent chromium prefers strongly octahedral coordination because of its large crystal field stabilization energy in an octahedral site.…”
Section: Homologous Series Of Superconductors
Stable Under High Pressurementioning
Under high pressure, a variety of elements can be accommodated at the cation sites in
the charge reservoirs of cuprate superconductors. Furthermore, high pressure allows the
insertion of higher number of CuO2 planes (i.e., the insertion period of a charge reservoir
becomes variable). Because of these effects, many new high critical temperature (T
c)
superconductors have been discovered under high pressure. In this paper, we will survey
their structural and superconducting properties. The role of high pressure and its effect on
the size mismatch between the charge reservoir and the CuO2 plane will also be discussed.
“…Vanadium has been already used as a charge reservoir substituent for mercury in Hg−12( n − 1) n −Ba and thallium in Tl−1212−Sr to discover (Hg,V)Ba 2 Ca n - 1 Cu n O 2 n +2+ δ ( n = 1, 2, 3) and (Tl,V)Sr 2 CaCu 2 O 7 . These studies suggest once more similarity of vanadium and chromium when they are used as a charge reservoir substituent because chromium can also substitute for mercury in Hg−12( n − 1) n −A (A = Sr, Ba) − and thallium in Tl−12( n − 1) n −A. − …”
A new series of high transition temperature (T c ) superconductors (Cu,V)Sr 2 Ca n-1 Cu n O y [(Cu,V)-12(n -1)n-Sr, n ) 3-7] was synthesized under a high-pressure/high-temperature condition of 6 GPa and 1300 °C. X-ray diffraction and transmission electron microscopy measurements revealed that they have M-12(n -1)n-type structures with M ) (Cu,V) and a stacking sequence of planes, SrO-(Cu,V)O-SrO-CuO 2 -(Ca-CuO 2 ) n-1 . Simple tetragonal lattices without any superstructures were observed for every member of the series implying a random arrangement of copper and vanadium in the (Cu,V) plane. Electron-probe microanalysis indicated partial substitution of strontium for calcium in the (Cu,V)-12(n -1)n-Sr phases. All the (Cu,V) phases gave large diamagnetic susceptibilities at a low temperature indicating bulk nature of superconductivity. The highest T c was found to be 107 K for the (Cu,V)-1234-Sr phase.
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