Simultaneous Structural, Magnetic, and Electronic Transitions in ${\mathrm{La}}_{1-x}{\mathrm{Ca}}_x\mathrm{Mn}{\mathrm{O}}_3$ with $x=0.25\mathrm{} \mathrm{and} 0.50$

The magnetic transitions in ${\mathrm{La}}_{1-x}{\mathrm{Ca}}_x\mathrm{Mn}{\mathrm{O}}_3$ ($x=0.25, 0.50$) were studied by synchrotron x-ray and neutron powder diffraction. For $x=0.25\mathrm{}$ the large $\Delta V=0.13\%$ at $T_C$ is due to the simultaneous insulator-to-metal transition. For $x=0.50\mathrm{}$ below $T_C$ we observed a drastic decrease of the $b$ axis and an increase of the $a$ and $c$ axes, due to a Jahn-Teller distortion of Mn${\mathrm{O}}_6$ octahedra. The ferromagnetic transition for $x=0.50\mathrm{}$ is accompanied by an unusual peak broadening terminating at $T_N$. This newly observed behavior can be explained assuming that multiple intermediate phases are simultaneously present in the sample.