  In the present paper we discuss about a set of geometric properties and
physical applications of a mixed quasi-Einstein spacetime$[M(QE)_{4}]$, which
is a special type of nearly quasi-Einstein spacetime$[N(QE)_{4}]$. Firstly we
consider a nearly quasi-Einstein manifold$[N(QE)_{n}]$ along with a mixed
quasi-Einstein manifold$[M(QE)_{n}]$ and study some geometric conditions with
respect to different curvature tensors on them. Then we consider a mixed
quasi-Einstein spacetime and study $W_{2}$-Ricci pseudosymmetry and projective
Ricci pseudosymmetry on it. Then we study the conditions $H \cdot S=0$ and
$\tilde C \cdot S=0$ in an $M(QE)_{4}$ spacetime, where $H, \tilde C$ are the
conharmonical curvature tensor and semiconformal curvature tensor respectively.
Next we consider a semiconformally flat Ricci pseudosymmetric $M(QE)_{4}$
spacetime and find the nature of that spacetime. In the next section we study
about some applications of a perfect fluid $M(QE)_{4}$ spacetime in the general
theory of relativity. Followed by we discuss about the Ricci soliton structure
in a semiconformally flat $M(QE)_{4}$ spacetime satisfying Einstein field
equation without cosmological constant. Finally we give a nontrivial example of
a $M(QE)_{4}$ spacetime to establish the existence of it.
