Solid ion conductor compound, solid electrolyte including the same, electrochemical cell including the same, and preparation method thereof

A method of preparing a solid ion conductor compound, the method comprising:

• providing a mixture comprising a lithium precursor and a holmium precursor;
• and
• reacting the mixture in a solid phase to obtain the solid ion conductor compound represented by Formula 1:
• LiaMxHoyXz Formula 1
• wherein, in Formula 1,
• X is F, Cl, Br, I, or a combination thereof,
• M is a metal element and is a divalent metal, a trivalent metal, a tetravalent metal, or a combination thereof, and
• 1≤a≤4, 0≤x<1.5, 0.5≤y≤1.5, and 4≤z≤9,
• wherein the compound has X-ray diffraction peaks at 30° 2θ to 33° 2θ, 33° 2θ to 36° 2θ, 40° 2θ to 44° 2θ, and 48° 2θ to 52° 2θ, when analyzed using CuKα radiation, and
• wherein a full width at half maximum of at least one peak at 40° 2θ to 44° 2θ is 0.35° 2θ or greater.