tikz: draw plot by given coordinates points

Question

I'm trying to draw, in a T=f(x) plane graphic, a curve passing through four points whose coordinates have been obtained experimentally. The x axis range is 0 to 0.5, the y axis range is 0 to 80. This is my attempt

\documentclass[11pt]{article}
\usepackage[utf8]{inputenc}
\usepackage{textcomp}
\usepackage[italian]{babel}
\usepackage[
  a4paper,
  margin=15mm,
  bindingoffset=2mm,
  heightrounded,
]{geometry}
\usepackage{amssymb}
\usepackage{amsmath}
\usepackage{mathtools}
\usepackage{float}
\usepackage{pgfplots}
\usepackage{xcolor}
\usepgfplotslibrary{external}
\tikzexternalize
\definecolor{verde}{HTML}{00C200}
\definecolor{gold}{HTML}{FFBF18}
\pgfplotsset{width=7cm,compat=1.14}


\begin{document}
\begin{flushleft}
\begin{tikzpicture}

\begin{axis}[

     width=12cm,
     %axis y line=center, 
     %axis x line=middle,
     xmin=0, xmax=0.5, 
     ymin=0, ymax=80,
     xlabel=x,
     ylabel=T(°C),
     xmajorgrids=true,
     ymajorgrids=true,
    grid style=dashed,
    ]

    \addplot+[scatter,color=black,ultra thick]
    coordinates {
    (0.31,63.5)(0.20,35.8)(0.10,30.1)(0.05,31.9)
    };
\end{axis}
\end{tikzpicture}

\end{flushleft}
\end{document}

I'm using MiKtex with Texmaker. I get this error message:

! Package tikz Error: Sorry, the system call 'pdflatex -halt-on-error -interaction=batchmode -jobname "LdCF1-figure0" "\def\tikzexternalrealjob{LdCF1}\input{LdCF1}"' did NOT result in a usable output file 'LdCF1-figure0' (expected one of.pdf:.jpg:.jpeg:.png:). Please verify that you have enabled system calls. Forpdflatex, this is 'pdflatex -shell-escape'. Sometimes it is also named 'write 18' or something like that. Or maybe the command simply failed? Error messages can be found in 'LdCF1-figure0.log'. If you continue now, I'll try to typeset the picture.See the tikz package documentation for explanation.Type H for immediate help.... \end{tikzpicture}

Can you help me?

Thank you in advance

Answer 1

Do you really need pgfplots for this?

\documentclass[11pt]{article}
\usepackage[utf8]{inputenc}
\usepackage{textcomp}
\usepackage[italian]{babel}
\usepackage[
  a4paper,
  margin=15mm,
  bindingoffset=2mm,
  heightrounded,
]{geometry}
\usepackage{amssymb}
\usepackage{amsmath}
\usepackage{mathtools}
\usepackage{float}
\usepackage{pgfplots}
\usepackage{xcolor}
\usepgfplotslibrary{external}
\tikzexternalize
\definecolor{verde}{HTML}{00C200}
\definecolor{gold}{HTML}{FFBF18}
\pgfplotsset{width=7cm,compat=1.14}
\usepackage{siunitx}

\begin{document}
\begin{flushleft}
\begin{tikzpicture}[x=24cm,y=0.1cm,>=stealth]
\draw[->] (0,0) -- (0.5,0) node[below] {$x$};
\draw[->] (0,0) -- (0,80) node[left] {$T\si{\celsius}$};
\draw plot[smooth] coordinates {(0.31,63.5)(0.20,35.8)(0.10,30.1)(0.05,31.9)};
\end{tikzpicture}
\end{flushleft}
\end{document}