Code:
\documentclass[11pt, oneside, a4paper,landscape]{scrreprt}
\usepackage[left=2cm, right=2cm, top=2cm, bottom=2cm]{geometry} % Ränder
\usepackage[latin1]{inputenc} % Umlaute
\usepackage[ngerman]{babel} % Sprache
\usepackage[]{scrpage2} % Kopf und Fußzeile ( Linie oben=headsepline, plainheadsepline)
\usepackage{graphicx} % einfügen von Bildern
\usepackage[small, hang, nooneline]{caption} % Bildunterschriften (noonelin = Linksbündig)
\usepackage{amsmath} % für Funktionsgruppe
\usepackage{colortbl} % Tabellen farbig hinterlegen
\usepackage{array}
\usepackage[light,math]{iwona} % andere Schrift
\usepackage{tikz} % Zeichnen in LaTeX
\usepackage{pgfplots} % Zeichnen von Diagrammen
\usepackage[version=3]{mhchem} % Chemische Ausdrücke darstellen z.B. \ce{CO2}
\usepackage{lscape} % darstellen von Querseiten
\usepackage{siunitx}
\usetikzlibrary{arrows,shapes,snakes,automata,backgrounds,petri,spy,decorations.pathreplacing}
\definecolor{blau}{RGB}{2,66,144}
\newcommand{\DiagrammH}{12cm}
\newcommand{\DiagrammB}{24cm}
\newcommand{\Pfeil}[2]{[color={black!20!white},->,>=stealth,line width=0.6pt](axis cs:#1)to(axis cs:#2)}
\begin{document}
\begin{figure}
\centering
\footnotesize
\begin{tikzpicture}[trim axis left,trim axis right]
\begin{axis}[
title=\large{\ce{CO2}-Beladung $\varphi$ $[\dfrac{g_{CO_2}}{g_{Oxid}}]$},
xmin=600, xmax=950,
xtick={600,650,...,950},
ymin=0, ymax=0.4,
ytick={0,0.05,...,0.4},
width={\DiagrammB},
height={\DiagrammH},
xlabel={\Large{Temperatur [\si{\celsius}]}},
ylabel={\large{\ce{CO2}-Partialdruck [\si{\bar}]}},
grid=major,
line width=0.6,
/tikz/background rectangle/.style={
fill=black!10!white,
draw=none
},
]
\addplot[black,domain=600:900]{3.58014E+04*exp(-0.5*(ln((x-7.84062E+01)/4.53161E+03)/3.74326E-01)^2)+1.27690E-03};
\draw \Pfeil{802.94,0.121}{802.94,0.1382};
\addplot[only marks,mark=diamond*,mark options={draw=blau,fill=blau}]coordinates{
(802.94,0.1160)
};
\addplot[only marks,mark=diamond*,mark options={draw=blau,fill=white}]coordinates{
(802.94,0.1432)
};
\draw (axis cs:815,0.1160)node[fill=white,fill opacity=0.7]{\small{\textcolor[RGB]{2,66,144}{blau1}}};
\draw (axis cs:790,0.1160)node[fill=white,fill opacity=0.7]{\small{\textcolor{blau}{blau2}}};
\end{axis}
\end{tikzpicture}
\end{figure}
\end{document}
sry für das etwas umfangreichere "Minimal"-beispiel
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