Indice
The Ruddlesden-Popper series of perovskites
The perovskite crystalline structure is the building block of many transition metal oxide families which are and have been of great interest for the past decades, e.g. cuprates, manganites, nickelates, ruthenates, titanates, etc.
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It is a building block of many different derived structure, being rather easy to alter it towards
- intercalation of electronically inert blocks, i.e. control of dimensionality, since an ideally isolated block would yield a perfectly bidimensional transition metal oxide layer, and
- intercalation of charge donor blocks, which yield charge tranfer to the transition metal oxide blocks
A typical series of related samples which can often be obtained is that known as the Ruddlesden-Popper (RP) series. shown in the figure. If, for instance, we take the La,Sr manganites, the RP chemical formula is:
{$ RPseries, \mbox{La}_{\mbox{n(1-x)}}\mbox{Sr}_{\mbox{1+nx}}\mbox{Mn}_{\mbox{n}}\mbox{O}_{\mbox{1+3n}} $}
the integer {$ n $} runs from 1 to infinity, and it coincides with the number of{$ \mbox{MnO}_{\mbox{2}} $} layers. The special case with {$ n=\infty$} coincides with the most studied pseudocubic compound, {$ \mbox{La}_{\mbox{1-x}}\mbox{Sr}_{\mbox{x}}\mbox{MnO}_{\mbox{3}} $}.
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The ideal La manganite series shown in this picture is made mostly of fictitious materials. For instance the n=1 sample is obtained only by partially substituting La by Sr.
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The following table shows the charge balance, under the assumption that the transition metal alone (Mn in this case) can display mixed valence:
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Ion
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Charge
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Multiplicity
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Total charge
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La
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+3
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n - nx
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3n - 3nx
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Sr
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+2
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1 + nx
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2 + 2nx
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(Mn)
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+3
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n - nx
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(3n - 3nx)
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(Mn)
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+4
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nx
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(4nx)
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Mn total
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n
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3n + nx
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O
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-2
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1 + 3n
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-2 - 6n
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TOTAL
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0
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Indice
