Heat ray shielding fine particles, heat ray shielding fine particle dispersion liquid, coating liquid for heat ray shielding layer, and heat ray shielding layer, heat ray shielding resin film, heat ray shielding dispersion body using them

Heat ray shielding fine particles containing calcium lanthanum boride fine particles represented by a general formula CaxLa1-xBm,

• wherein a value of x in the general formula is 0.001≤x≤0.800, and a value of m is 5.0≤m<6.3,
• an average dispersed particle size of the calcium lanthanum boride fine particles is 1 nm or more and 800 nm or less,
• a shape of each fine particle of the calcium lanthanum boride fine particles satisfies at least one of the following:
• 1) when scattering intensity of the calcium lanthanum boride fine particles diluted and dispersed in a solvent is measured using small-angle X-ray scattering, value Ve of a slope of a straight line is −3.8≤Ve≤−1.5, which is obtained by double-logarithmic plotting of a relationship between scattering vector q=4π sin θ/λ and scattering intensity I (q),
• 2) the particle shape is a flat cylindrical (wherein a diameter of the bottom circle is d and a height of the cylinder is h) shape, or a flat spheroidal (wherein a length of the long axis is d and a length of the short axis is h) shape, with a value of aspect ratio d/h being 1.5≤d/h≤20.