We report a thorough study of ${\mathrm{Y}}_{0.7}{\mathrm{La}}_{0.3}{\mathrm{VO}}_3$ single crystals by measuring magnetic properties, specific heat, thermal conductivity, Raman scattering, x-ray and neutron diffraction with the motivation of revealing the lattice response to the spin-orbital entanglement in $R{\mathrm{VO}}_3$. Upon cooling from room temperature, the orbitally disordered paramagnetic state changes around $T^{*}\sim 220$ K to a spin-orbital entangled state which is then followed by a transition at $T_N = 116$ K to $C$-type orbital-ordered (OO) and $G$-type antiferromagnetic ordered (AF) ground state. In the temperature interval $T_N<T<T^{*}$, the ${\mathrm{VO}}_{6/2}$ octahedra have two comparable in-plane V-O bonds which are longer than the out-of-plane V-O1 bond. This octahedral site distortion supports the spin-orbital entanglement of partially filled and degenerate yz/zx orbitals. However, this distortion is incompatible with the steric octahedral site distortion intrinsic to orthorhombic perovskites. Their competition induces a second-order transition from the spin-orbital entangled state to a $C$-OO/$G$-AF ground state where the long-range OO suppresses the spin-orbital entanglement. Our analysis suggests that the spin-orbital entangled state and $G$-OO are comparable in energy and compete with each other. Rare-earth site disorder favors the spin-orbital entanglement rather than a cooperative Jahn-Teller distortion. The results also indicate for ${\mathrm{LaVO}}_3$ a $C$-OO/$G$-AF state in $T_t \le T \le T_N$ and an orbital flipping transition at $T_t$.

• Received 29 August 2018
• Revised 4 June 2019

DOI:https://doi.org/10.1103/PhysRevB.100.184423